Shapeways has a whole library of items that other people have designed that you can print. I ordered several as stocking stuffers at Christmas. Holding them in your hand is a good way to get what this whole 3D printing thing is about.
The items I ordered:
http://www.shapeways.com/model/24470/gyroid.html
http://www.shapeways.com/model/335195/the-code-prize-fire-co...
http://www.shapeways.com/model/683524/super-mario-mobius-str...