Splitlid is doing some nice 3D renderings of peoples house ideas and I didnt want to hi-jack his thread so heres an online floor planner.
As its web based its going to depend on your connection for performance and you'll need to sign up for an account if you want to do anything more than play with th demo. I had a quick play with a demo and it seems fairly straight forward, drag stuff like walls to make them bigger/smaller with menus for stuff like doors etc.
No idea if you could plan a house completely with it but if you want a quick idea of how your dream house might look and work out a floor plan it might be of use to someone.
Create floor plans, house plans and home plans online with Floorplanner.com