My daughter is 2 1/2 my in laws just gave her a hand me down doll house and she adores it. We don't have any dolls or furniture for it yet (which I know she would love to have because the library has one and she loves to play with that sutff there). She just uses her little people as toys in it and she adores it so I give a big vote for a doll house. Ours is completely different but if I had opted for a new one I would have gotten something like this:http://www.growingtreetoys.com/product/7771
If you look on the menu at growing tree toys there are tons of other dollhouses to choose from.
My daughter also really loves dress up clothes. I have a bunch of hand me down dress up clothes that were generously given to us.
I would definately invest in a box of dress up clothes for that age group. Some ideas for the dress up box:
Doctors(white coats,scrubs,paramedic type costumes),firefighters, cooks, any other type of professional your kids might like to dress up as.
Renaissance type outfits (super fancy dresses, pantaloons,bloomers,capes) google renaissance im sure you will get tons of results
Fantasy stuff (unicorns,knights,princesses,fairies,dragons)
Shoes of any type that is different, doesn't even have to be their size
Abstract play stuff like play silks
whatever else you can think of this was just some random ideas to get you started
atoygarden.com has some good dress up clothes but you will probably have better luck searching costume by costume or looking at goodwill for stuff that will work.
A wooden kitchen is a great idea, my daughter doesn't have one but she loves to pretend to cook and will do it with whatever toys she has available (little people become "chicken" ect). We would love to have one, I say go for it!
My mom bought my mom some automoblox for christmas she loves
them. They are so cool we like to play with them too. My husbands 10 year old foster brother even liked them so I am hoping they will last a long time. Here is a link, you can buy them at tons of places cheaper than the main site though with a little searching. http://automoblox.com/
My final suggestion is art supplies. Or "art" toys my daughter has a doodle pro that gets a lot of play time but what she really loves is finger paints (crayola ones wash up really easy), crayons, markers, stickers, construction paper ect ect use your imagination. If we had the money and space I probably would get her some sort of an art desk her size, right now she does art at the kitchen table but boosters are uncomfortable and shes a little too short for the table.
Hope that gives you some ideas!