Are those book shelves in between? Why not create a lounging/reading area with a lounge chair and ottoman, a reading lamp, a rug and a small side table to put your cup of hot chocolate?

Assuming that you're allowed to paint - PAINT! Go for a bright accent color that will act like a large visual stripe (think vertical), to mark the two as separate spaces.

Ditto cozy reading area--a mini library space. Or an art gallery with two wall-sized paintings. I like the idea of bold paint in there, too.

grand piano :)

Since the couch isn't facing an entertainment center, can't you cut the room with the couch, turn its back to the long space to close in a conversation and relaxing area?

I like those long spaces because I have a piano to put somewhere and that's where it fits well.

Put an island in the kitchen and move the table into the open space.

It seems like you have centered the couch on the door across but I don't think you have to. I would shift the couch and rug further into the center of the room (especially if you are going to rely on that table as an entertainment center eventually). Also, is your kitchen seating a booth? If not then you really could bring it out into the middle to fill the space. Alternatively you could get a bar cart, or you could turn the couch as someone else suggested and put a sofa table or buffet up against the back of it for additional kitchen storage. Good luck!

Is there an area in your home that you are missing? A cozy reading nook? Desk space? Storage? I'd look at what functions you would like your home to have that it currently doesn't, and figure out a way to use that space for it.

I also agree that you could move the existing furniture around to take advantage of some of that space.

Create a "hallway" at the entrance, maybe using that rolling bookcase. Not only will it break up the spaces, but it will reduce the abrupt entrance into the living space.

I second @Therese Z 's idea! Turn that couch so the back of it faces the kitchen. Maybe add a console table behind it? Put a bowl on it to be a "catch-all" for your keys & change when you walk in the door. It would also be a good spot for guests to drop their purses. You could even add a lamp and a stack of books to dress things up a little. That would definitely help define the living room space more.

I also liked @lella 's idea of a island in the kitchen (permanent or not) to fill some of that empty floor space in the kitchen.

more seating

It looks like it would make a great dining area with a round table and four chairs. Then, purchase an island on castors for the kitchen to go against the wall where the table is currently, which you can pull out closer to the sink/stove for more work space if you need it.

I LOVE the idea of turning the couch so the back is facing the kitchen, and creating a little entry way, book storage etc spot. I guess your concern is that the path that is left might be a little tight (looking at the length of the couch). A semi-permanent island could also work really well, and add some extra seating for guests. All in all, a great space with lots of light to work with!

I agree with lella, this looks to be an open plan for kitchen, dining and livingroom. You are missing the dining component in between. Move the round dining table to that center space near the bookcase, and add an island in the opening to the kitchen, like this

http://www.ikea.com/us/en/catalog/products/00058487/

Kitchen island with bar you can pull stools up to

Dinning room! Where your table is now can be a little breakfast/coffee nook.

Is the room long enough for bowling? Do you like to bowl?

I second SelfridgeDesign & Iella's responses. I would go for a larger free standing island like http://www.ikea.com/us/en/catalog/products/00116996/
This will give you more work space and you can put seating on the other side. To make it match your cabinets you could probably paint the legs black/brown.

Do you want to keep the open sight lines between the living room and the kitchen? You could also create separation by having a two sided open bookcase / divider like http://www.ikea.com/us/en/catalog/products/70201811/ which you will be able to use like a wall. Put a chair and an end table on one side and you have a libray/reading nook. Or put a little desk and you have a laptop/writing area. The open cubbys will still keep your flat looking open but just help define the space a little better.

Looks like it was built to be a semi-formal dining room to me. Not that it means you need to use it that way, but I suspect it's the reason it's there.

I don't like it when people break up a room by blocking it with a sideways couch or tall bookcase (I'm not a new-agey kind of person, but it does feel like it blocks the energy). If you feel the same, maybe consider bringing two chairs between the living room & kitchen (facing the living room). That's what we did... it helps to define the space without making it difficult to enter.

Second thought would be to add a small island to your kitchen area... you have so much central space, I'm jealous!

Rearrange the living room by turning the sofa, coffee table and rug 90 degrees. In other words, the sofa will be parallel to the wall with the narrower window. However, pull the sofa away from the wall so it floats a bit, and perhaps put a credenza behind it. That way your entire living room will face into the center of the space creating a nice book end to the kitchen. Then move your table and chair set up to the middle of your blank space. I think this will help all three areas flow more seamlessly.

Our house is shaped like this, and I have a round dining table & 4 chairs there. Our formal dining room is where your eating area seems to be from the photos.

A bar.

What about a hallway rug with a cool print that floats from door to wall and a great piece of vertical art at the end or armoire for shoes/bags/coats or desk? Your kitchen looks like it could definitely use an island or bar. Can that bookcase go where the small table is now on the wall next to the window? The table looks out of proportion there.

I agree with the others, You need an island in the kitchen with some barstools and move the couch from against the wall to the kiddy corner side facing the smaller row of windows. Also in agreement to put the sofa table behind it and perhaps a rug to cut the two spaces apart.

Right now, everything is against the walls, and it's my personal opinion, but I think it looks really boring and flat that way. Which is why you have so much empty space.

I would add a rectangular dining table and use the dining are you have now as a little home office.

What about trying something similar to the third picture? Pull the couch away from the wall, buffet behind it, etc, then bookshelves, hanging room dividers, something to act like a "wall" to separate out the two rooms?http://sf.curbed.com/archives/2012/10/23/noe_valley_victorian_oozes_coolness.php

the empty space is beautiful, leave it empty.

We have the same, except it's an L shape. We use it as a dining area, for when we have more than just the family (currently only three of us, and we sit at a little kitchen table, like you have).

Does the door on the left lead to a hallway? If so, take off the door; seems unnecessary. Wall space (on the door side)? Mini art gallery maybe. Desk or a small reading/lounge area. Depends on your level of entertaining; if a lot of people etc. are going to be going from LR to kitchen (and maybe carrying stuff) don't block it off with furniture too much.

a cafe table maybe 36", right in the center. put a vase or something in the middle for vertical definition. stack some cool books on it.

or add a capiz curtain across the divider doorway starting on the sink wall.

or just enjoy the space...

less white will make it seem a bit smaller and less empty

you could also.. turn the couch to be a barrier and put a small sofa table behind it.. to help define the separation better

If this were my space, I would take that bookcase and move it over to where that little low white table is on the left. Then put a little bar cabinet where the bookcase was, with a mirror above it and a nice lamp on top. Also put a rug on the floor in the entranceway, and another chair with its back to the bookcase.

*A friend of mine says when all the furniture is up against the wall that it looks like "they're under arrest"...

Enjoy the open space. Why must you fill it up or separate it off? You could, however, add another chair in the living room area.

Otherwise, it's always great to have more prep space in the kitchen, hence an island with seating would work. This would be inviting to guests who often gravitate to the kitchen.

when you're lucky enough to have this kind of excess space - FLOAT your furniture off the wall. A wide console behind the sofa perpendicular to the kitchen could be a home for your laptop, a work space, etc. But for the love of God, please, please no bright accent wall paint. It's not 1998 anymore. :) enjoy!

My first thought was a Saarinen table with flowers on it.

My second thought was something could be done with another rug - to delineate the space.

My third thought was a substantial kitchen island and two chairs with their backs to the kitchen.

If the door that's open in your photo is the front door, create a landing strip. Delineate the space with a rug and use something like Ikea's Expedit that would still let light in and can hold keys, mail, etc.

looks like a good space for twirling

A couple of suggestions:
1) Turn the couch sideways, as a few people have suggested, and shift the living room layout accordingly. You could move the chair to the other corner, get an ottoman for it, or both.
2) Move the white rug into the empty space and get an additional rug for your living room. You seem to have an excess of squares and rectangles in that area, so I'd recommend going for something round, oval, or asymmetrical and curvy.
3) I'd definitely recommend putting together some sort of kitchen island configuration to break up all that empty space in the kitchen. A countertop that sticks out far enough to slide a couple of barstools under would give multiple people a place to sit down while prepping food. It doesn't have to be cluttered or super expensive. I've seen some pretty creative setups done on the cheap over on IKEA Hackers.
4) As for the empty space... Moving the rug to it will make it seem a lot less empty right away. What you do with the space then is up to you. A comfy chair with a footstool right in front of the bookcase would be cozy, or you can set up a home office area, a music listening area, or a place to show off whatever you might happen to collect.

Depends on what you like to do. IF you often serve big family meals, or like to have people over for dinner, consider making it into a dining room as others have suggested. If, on the other hand, you PLAY the piano & have one or want to have one, the area could become a music room, as people have also suggested. IF neither of those are of much interest to you, I would think about turning the space into a "library" and sitting area, where a few people could read or relax or have a conversation. By arranging objects, you could delineate these areas by appropriate arrangement of furniture, rugs, etc.

Yoga!