On the Cool Tools mailing list, Wired editor-in-chief Chris Anderson (a hardcore maker of cool things, like DIY Drones, and founder of GeekDad) heartily recommends Autodesk’s 123D:

Printing in 3D is now no more complicated than printing photos in Picasa. First you design something in Autodesk 123D (in my case, my first project was a device housing prototype). Then pick “Make” from the menu. You can print your object on your desktop printer, like a Makerbot (moderate quality, now), or you press another button to have it printed (high quality, later) on a commercial printer. Enter your credit card (my prototype, shown here, cost $24) and a week later, it’s delivered to your house. Wow.

Best of all, 123D is free. This is the future of fabrication.