PlanningWiz is a well-built online app for building floor-plans. While I don’t love the look of the interface it actually works very well. Some clever UI ideas in there.
Alex is CEO of Sideshow , an award winning creative agency. You can read his blog here.
You might want to take a look at the new version of Floorplanner (http://beta.floorplanner.com) it does 2D and 3D