Gliffy is a free online service that allows you to create and share charts, diagrams, graphs and maps on the web. It’s that last one that’s interesting: Even with a very limited object set (chair, desk, bed, table, etc.), it’s fun to fiddle around with.
Here’s a sample image of a floorplan. You can also export your creations as images, which could be printed as handouts, or share them online (handy for a play-by-post game).
It’s currently in beta, with plans for a paid version and an ad-supported free version. You have to sign up, but there’s no confirmation process. (Via Vitaly Friedman’s Notebook.)