Check this one out from Lillian Vernon. I liked that it was gender-neutral, simple, and that it came with the accessories. Plus the price is nice.

Although my two-year old son loves playing with the dollhouse at his daycare right now, I'm not sure for how long and I didn't want to invest too much money into it.

http://www.lillianvernon.com/catalog/product_display.jsp?pdId=11445&name=Wooden Dollhouse %26 Furniture Playset&parentCatId=2&catId=246&subCatId=380

My friend makes small dollhouses (and the little people to go in them) that are painted with non-toxic paint. I think they're lovely:
http://www.etsy.com/view_transaction.php?transaction_id=9631685

Hi Katie,
What about using a "bookcase dollhouse"? It would be flexible because it could be used for whatever your kids are into at the time: dollhouse, fire station, hospital, barn, school, etc. You could put a basket on one of the shelves to hold accessories so that it cleans up quickly, and when your kids have grown out of the doll house phase you can use it as a bookshelf in their room.
-Here is a gender-neutral one from pottery barn that is pretty pricey:
http://www.potterybarnkids.com/products/pk128/index.cfm?pkey=xsrd0m1|12|||1|||||||dollhouse&cm_src=SCH
-And here is a cheaper version from target (it has pink trim, which you could paint with non-toxic craft paint):
http://www.target.com/dp/B000ES272W?activetab=Guest Reviews&sortReviews=%2Brating
Or if you're crafty, you could make one. It doesn't seem too difficult, just straight boards and a jigsaw to cut out windows and doors. You could even add a staircase, trap door, etc. The downsides are that it would be a more permanent fixture than a dollhouse that could be stashed away in a closet and it would have to be anchored to the wall. But it also wouldn't take up a lot of floorspace.

I like these
http://www.growingtreetoys.com/brand/ryans-room

Plan makes a contemporary one that isn't huge - it's not as cheap as others, and you have to buy furniture separately: http://www.giggle.com/p/21146/Contemporary-Dollhouse.aspx

Get the Plan Toys Chalet dollhouse (the one on the left) -- it's great, because you can move around the components, and comes with the furniture (for about $125, which isn't bad).

We got the Terrace dollhouse (the one on the right) before the Chalet came out, and it is annoyingly deep, thus difficult to play with.

We got it for our daughter first, but our son loves playing with it too.

p.s. we find it rather sculptural and attractive in our living room

farleece-that one from Lillian Vernon looks great. I have never seen it before and the price cant be beat. Thanks for the link!

oooh, how about this one:
http://www.creativityinstitute.com/EducoMyRooftopGardenHomeFurnishedDollhouse.aspx

Ok. Here's another inexpensive but cute one - and it's a hospital. I'm leaning towards this one.

http://www.lillianvernon.com/catalog/product_display.jsp?pdId=11454&name=Electronic%20Hospital%20Playset&origin=crosssell

Oops, although it is plastic and I'm not sure about the lead factor.

i guess the furniture is not gender neutral, but i like this one.

http://www.landofnod.com/family.aspx?c=9573&f=4847&q=dollhouse&fromLocation=Search&DIMID=400001&SearchPage=1

So get him a "girly" doll house... if he likes it, who cares? Break down some gender stereotypes & get your kid a fun toy all at the same time!

What about this one from Melissa & Doug?
http://www.melissaanddoug.com/dyn_prod.php?p=795

$99 on their site, but you can find it on Amazon for about $70 shipped. I'm considering it for my 2 1/2 y/o boy/girl twins.

I love the Plan Toys Tree House. It's beautiful and would work equally well for plastic dinosaurs, action figures, wood-nymph fairy dolls, little people, or the plan toys dollhouse dolls.

See it here:
http://www.oompa.com/cgi-bin/item/PL7152

We have the Melissa & Doug wooden treehouse for our 3-1/2 year old boy:

http://www.amazon.com/Melissa-Doug-Classic-Wooden-House/dp/B000KEMCQ6

It looks cool and he loves it, but holy crow, it takes up a LOT of floor space.

Looks like Duluth Trading, which sells the Design-By-You Doll House, is offering Free Shipping until December 1. Use code T28WE70P.

http://inhabitshop.com/index.php?main_page=product_info&cPath=109&products_id=660

I had to post this one I just stumbled across. The orange plexiglass makes it so modern and cool. Imagine if you rigged up a few mini lights inside! It would be a very modern lamp/light installation in your living room when the kids weren't playing with it. But it ain't cheap :(

Land of Nod has a cool one.

http://www.landofnod.com/family.aspx?c=9573&f=4847&q=dollhouse&fromLocation=Search&DIMID=400001&SearchPage=1

There's also this "tree house" as they call it. I want this one!

http://www.livingplaying.com/thb001.html

Here's a cool Melissa and Doug folding dollhouse. Only $60 from Amazon (free super-saver shipping). It reminds me of the vintage Fischer Price dollhouse that I had when I was a kid.
http://www.amazon.com/Melissa-Doug-Fold-Go-Dollhouse/dp/B000067BID/ref=sr_1_12?ie=UTF8&m=AFY0JJAJVXDYO&s=toys-and-games&qid=1228400396&sr=1-12

Thanks for all the great suggestions! I'm going to have a hard time choosing now!