www.RoomBuddies.com
Roombuddies helps you find a roommate, or find a room to rent. Simply enter your requirements and search for your ideal roomie! easy search!

www.sublet.com
huge database of apartment rentals and rooms! very well detailed search possible with maps.

www.lodgis.com
find a flat in NYC ; lots of very nice appartments in the best NYC areas, for all budgets..

www.roommates.com
Nicely made site, easy to use, free login! has got lots of ads, very precise area search possible, easy to use.