Sierra (the computer games company) used to have a nice software package to do this that was like $30, but Sierra's out of business now, so I don't know where that program got to. Similar programs I remember from the time were made by Broderbund and Better Homes and Gardens. Check them out.

However, yeah, there are a bunch of programs that will help you do this. Search for "floorplan software", "interior design software", etc.

While searching for some of this, I stumbled across some other things that look useful. RoomArranger. How about this online tool?