Gloria Furniture -- These are plastic furniture sets. Mostly pink plastic, but some of the sets (like the dining room and bar sets) come with really great dishes, silverware and glasses, etc. props. Assembly required. (And unless you like pink, repainting required... I put two coats of MSC on, then several coats of acrylic to create the brown 'bedstead' that's in some of my pics. Spray painting might work better.) Note: The sets themselves are cheap, but the shipping is exorbitant. But if you can get a deal (like buy three, get one free), it's probably worth it. And again, the props are great!
Ebay often has "Barbie Furniture" lots -- people who are cleaning out their attics and getting rid of kid stuff. Sometimes this stuff isn't in the best of shape. Sometimes you can find some incredibly wonderful hand-made pieces that are well worth the price. It's mostly a matter of keeping your eyes open. Also now that the weather is getting better, keep an eye out for yard sales (but get there early. You're competing with parents of little girls with Barbies!)
Recommended: Ebay seller
http://stores.ebay.com/DOLL-CLOTHES-RACK?_rdc=1 -- sturdy, well-made stuff, the only drawback is the limitation of colors (basically little-girl pastels or little-boy cammo).
And if you have the budget for something slightly fancier:
Victorian Doll Furniture -- these are incredibly beautiful. Not cheap. But really well-made. (Also the room-box instructions I used to make my set are from this site.)
I've also found some PINCUSHIONS at Joann fabrics that are shaped like armchairs -- and they're a perfect size for 1/6 dolls. If you like craft/sewing projects, Simplicity has patterns for "fashion doll" furniture that are pretty nice too, using mostly foamcore board and fabric, and a little stuffing.
And of course, there's always the Barbie/Bratz furniture playsets that you can find at any toy store -- keep your eye out for sales. Good luck!