Good floor planner program?

Sweet Home 3D

Sweet Home 3D is a free interior design application that helps you place your furniture on a house 2D plan, with a 3D preview.

I love Google SketchUp. It's not made specifically for this application, and I'm sure there are others, but if you're looking for simple, this is the ticket. And who can argue with gratis?

I guess Wine kind of sucks, though.

It's not open source, not really a program, and the free version is limited, but I've found the flash-based floorplanner.com to be simple and a pleasure to use.