What a great question! I know that I can come up with a pile of stuff for you, but frankly, need more information.

What subject do you teach? What is your classroom like -- what sort of classroom furniture do you currently have (blackboards, desks, tables, bookcases, etc., etc), what sort of construction materials are used (walls, floors -- is the room carpeted? are the walls cinderblock? How easily can you hang things?)?

Love the ceiling.. Is that oak?

For plants, I have had great success with snake plants, zizi plants, pothos, and aloe vera. Otherwise, I would choose natural materials as much as possible like solid wood. I try to use framed artwork along with original pieces. It is wonderful if the decor can tie into the curriculum. (I teach Waldorf fifth grade this year and have drawn from ancient civilizations for my decor.) You can find some good small storage options at Ikea that are affordable and look nice.

Wow. Your school has air conditioning?

Check to see what the guidelines are for what can be brought into your classroom because of fire codes, etc. Our school district states that we can't bring any kind of upholstered furniture because of fire codes and allergies.

I know...it's tough.

@mschatelaine could you forward me some ideas?! I was actually talking with a coworker about this exact thing, so it's perfect timing to see this post.
We are in an inner-city arts high school in Washington DC and teach Math (I also teach Physics).

Yoga mats with throw pillows. Easy to stack out of the way but kids can (and when at home often do) stretch out on beds to do writing or reading. If the chairs are hard (I was skinny and school chairs were an agony) ask kids if they want to bring in seat cushions. For that matter, ask kids for suggestions on ways that would make them feel more homey. With plants just make sure not to bring any that are poisonous. I think wall art is a great idea but why not have art the kids make. Also engage them in setting it up. There's a lot to learn in the doing. Hang a beautiful rug on the wall. Or have the kids bring in a piece of fabric or old clothing they like but no longer wear, cut it up and put a piece of each together inside a frame or frames. Crazy quilt art. Include them. If they help choose or create what is there the more at ease and invested they will be in everything about your class.

Fire codes tend to be strict about what and how much teachers put on the walls. . . .

Hi, I'm a middle school teacher too. It's hard to make a classroom, that you have 200 to 300 students move in and out of, daily, feel like a home. Elementary students, have a stronger sense of home and ownership in their classrooms because they stay in one classroom most of the week. The austerity and formality of most middle school classrooms compared to the sense of community in an elementary classroom feels very real to me. Middle school students, depending on the type of scheduling the school has, can enter up to seven different classrooms in a day.
I've tried to give my classroom a homey feel. I used to have a couch in the side of my room. The students liked that for a comfy place to go to for partner or small group work. I'm not big into the florescent lighting found in most public education classrooms. I prefer full spectrum lighting, but I have yet to see a public school that uses it. You might be interested in an article you can find on-line called "Light: An Element in the Ergonomics of Learning". I knew a kindergarten teacher who had a fundraiser just so she could replace all of her florescent light bulbs with full spectrum ones. The few Waldorf classrooms I have been in used as much natural lighting as possible. The curtains were always open (if there were any) to let in as much sunlight as possible. I do the same in my classroom and turn on as few of the overhead florescent lights as possible. I like to have a small lamp on my desk, which I keep turned on throughout the school day. It gives the room a homey touch. You could also place lamps elsewhere in your classroom. I found a video on You Tube called "Feels Like Home: Classroom Culture Optimizes Learning" which you might enjoy (ah, the joys of private school). Philodendrons always grow well, in my classroom, as do succulents. A colleague of mine has a planter on rollers which she puts outside her door every morning. I try to use as few plastic containers as possible and am constantly on the lookout for square and angular baskets I can use in their place. I never pay retail. I do yard sales and thrift shops. I also constantly edit.
I am thrilled to know Maxwell used to be a Waldorf teacher. I love it. My nephew went through a Waldorf school and I took a course on Waldorf education for public school teachers (almost sounds like an oxymoron). ONE of the many things I loved about the Waldorf classrooms was their Lazure painted walls. The color of Waldorf classroom walls are a different for each grade level. It's all very intrinsically woven into Waldorf's approach to addressing the whole child. There is info on the internet about this type of painting. Another thing I noticed in Waldorf classrooms was the connection to nature. The use of sunlight, wooden furniture, simplicity, organization and beauty makes for an inviting, calm learning environment. Also, I noticed there was breathing space in the rooms.The rooms were not cluttered. The students are taught to respect their environment and their belongings in a reverent conscious way. It's a very different feel. My nephew is in a private college-prep high school, now. It took him about two years to adjust, but he is doing quite well. I'm glad he had his initial years in a school such as Waldorf. He's a really well adjusted young man. I attribute a lot of this to the eight years he spent in a Waldorf school. Very comfortable with himself.

When I was a classroom teacher, I decided to bring elements of my home into my middle-school classroom as well. My students and colleagues found my classroom to be refreshing and unique. I would post pictures but my hard drive crashed a few months ago.

Anyways, there are 2 things I keep in mind when shopping for myself and arranging things in my house, and here’s how I adapted these things for my classroom.

1. A home feels personal and special.
The “homey feeling” you’re after won’t come from merely bringing furniture and other stuff from your house. That will likely just make your classroom feel like it’s a place for your leftover things.
+ If possible, paint a cool and soothing color, like a light blue or green.
+ Cover all bulletin boards with fabric to bring warmth and texture. Find an interesting pattern/print, display it prominently. In other areas, use solid-colored fabrics in the same color story (or use paper if money’s tight). Use a solid color border for your printed fabric and vice-versa.
+ Avoid storebought decorations; make your own signs and posters. Storebought classroom decorations have a generic, yet distracting quality to them. They’re also expensive. Use your best teacher handwriting, block lettering, and figure drawing on posterboard that you’ll laminate and hang. Students will respond to the care and energy you invested by treating the classroom environment with respect.
+ Curate your displays. Whether it’s informational or inspirational, choose items (including student work) relevant to your lesson/unit, and rotate the old stuff out. Your early finishers and talented in visual art students will be more than happy to make poster size versions of figures and illustrations from textbooks.

Remember that the classroom is an environment that YOU create, but is FOR your students. Your students will respond better to a room that was clearly made for them, rather than being trapped in part of your house.

2. Everything should go together.

+ Pull inspiration from the classroom itself. You can’t force an autumn color palette on a light blue classroom. Use the same wood tones that might already be present in furniture, shelving, or cabinetry. Adopt a design aesthetic that complements the building’s construction. Since many schools were built mid-century, it’s hard to go wrong with that. Bring in pieces that are conducive to learning--- couches, rugs, and throw pillows are great, but only if you know they won’t distract your students.
+ Use contrast very sparingly and very intentionally. I wanted my classroom rules poster to stand out in my light green classroom so I constructed one with bright (but not neon) yellow posterboard and black lettering. The idea is that if anything stands out, it stands out in a good way for a good reason. Go overboard, and you won’t be able to use contrast to highlight important aspects of your classroom.

...I hope these ideas help. Also, 3M Command Strips/Hooks are your best friend!

Wow! Some really great comments here!

As everyone has pointed out, fire regulations are key, and must be respected. Thus, contract-grade wallpaper, fabrics, rugs, etc., because of their fire safety ratings and durability would be one suggestion.

Lighting is definitely key -- table lamps make things cozy (again though, have to check the fire code), and full-spectrum lights and as much day light as possible.

Try to match the color and decor to the topic. I still remember my grade 8 English class, which was my favourite class in school, ever. Our teacher had painted the entire room a very dark, deep brownish-green (think Donald Kaufman Colors DKC 65). There were no desks, but rather long seminar tables, 2 of them, and comfy seats. The requisite bust of Shakespeare, dark heavy curtains (no fire codes back then obviously), and framed art work. It was like stepping into another world. We used to watch movies in that class (he had a vcr waaaaaay ahead of anyone else -- this was 1978/1979), and yes, there was a red Persian rug on the floor.

For physics and math, you would try to create a room that is stimulating in completely the opposite way. Bright colours, like touches of true red and Yves Klein blue, as well as yellow for math and purple for physics. Perhaps a pure black wall with brightly coloured things on it.

As posted earlier, for math and physics, I would make sure that there is a lot of air-space, and as little clutter as possible. Natural woods would be beautiful, the full-spectrum and natural light. Museum-framed pictures on the walls, not just posters tacked up, would make a big impression. And clever, unusual subject-matter artifacts, the kind which could pass for a sculpture at home but which are really a teaching tool would be a brilliant idea.

My favourite school design is the German School of Geneva. In Europe, there is a lot more value placed on how physical design supports the intended activity in a space, and some of the schools (both public and private) are quite stunning.

The German School is private (although funded in part by the German government for German expats living in Geneva and who desire their children to follow the German curriculum). The school in infused with natural light, exciting contract cabinetry and furniture, hardwearing but beautiful surfaces, and lots of artwork, framed in museum frames. Very, very different from a North American school. An interesting design alternative.

http://www.dsgenf.ch/fr/galerien/galerie-photos-du-batiment/

Museum frames:
http://www.metroframe.com/framing-advice-final-assembly/

Hi
I'm a school psychologist in a high-school, and I think it's a shame how we neglect the environmental aspect of learning envirnoment (expecially compared to elementary school). So, I'm glad that you're eager to put some effort in it, and belive you've gotten some great tips here.
What I'd like to add (or stress out more, I think someone mentioned it) is that beside making a homey atnosphere for your students, I'd encourage you to find a way to let them do something for themselves. We all have the need to personalize our environment in order to feel like it's our and that we belong there. I could go on and on about it, but if you're interested in the idea, you could check up my blog about environmental psychology, mindshapedbox.wordpress.com where I just recently wrote about the effects of classroom personalization, school building condition, home environment etc., on children's academic achievement, self-esteem, etc. Btw Maxwell's teaching experience inspired me, too.

*what I meant in the first sentence was "environmental ascpect of learning".

What a wealth of information you have received, Randi. I want to thank all of you who posted, here. There are so many great ideas I have never thought of. Love the ideas RE keeping the room simple, purposeful and aesthetically pleasing. Thanks for asking this question, Randi. I could talk about this topic forever.

At the beginning of the school year, my teacher-daughter puts a small display of personal items on a shelf. They include a family snapshot, a middle school photo of herself (for laughs), a pair of toe shoes, a toy violin, and mini mascots from her undergrad and graduate schools.

She said it helps break the ice.

I think the best people to ask are the ones for whom you are making the room home-like. Your students will be full of ideas and when you use them, they will feel a sense of ownership. If you are a language arts teacher, you could have them write an essay on their ideal room and then surprise them by incorporating elements from their work into the room.

I taught high school for 15 years, and the classroom environment was always really important to me. Some of my favorite things: open shelves that ran the length of the walls with lots of things for students to explore (I had boxes with interesting objects in them, books, sculptures) - all not "too precious" so they could touch and explore them - framed art posters that I picked up at garage sales - either propped on the shelves or hung on the walls - frames make them look so much better! I had a lot of large plants - full sized 6' trees - lots of houseplants can live just fine in the classroom as long as they're fed and watered - here are some pics of my classroom --
https://s3.amazonaws.com/files.digication.com/Maf50516e749214395f0984e3a306b81b.JPG

https://s3.amazonaws.com/files.digication.com/M3a51efb02f399c78bda72323e3cab614.jpg

http://www.flickr.com/photos/8696728@N03/6354138911/

http://www.flickr.com/photos/8696728@N03/6354138827/

I know I had a really big classroom, but a lot of this stuff doesn't take much space! Those are two different classrooms, but the same decorating ideas are in both. My classroom was always a spot on the principal's tours with visitors because it was such a fun environment.

My husband is a teacher, and one year I helped him decorate as he set up for the year. His school was previously a sardine factory, so each room was essentially a concrete box! I arranged a few bookcases in a U-shape at one end of the classroom to create a "library nook," complete with a colorful 8x10 jute rug (dirt-cheap from Craigslist), so they would feel comfortable perusing books there. If I'd had a couple of floor pillows or a bench, that would have been even better! Then around the periphery of the room, we made "boards" from dark brown butcher paper (the kind that's 3' wide and comes on a roll) to made paneling and moulding. He said it took a few teachers several visits to his classroom to realize it wasn't actually part of the room! Good luck - it's hard to decorate super duper cheap, but it can be done!