Anyway, there's a "pen" thing that, by extruding plastic instead of ink, lets you draw in 3D. It's on Kickstarter right now. It's called the 3Doodler, and it is to a 3D printer what a regular pen is to a regular printer: it lets you sketch out a rough outline (or wireframe) (or a detailed sketch, or a beautiful drawing, depending on skill level) in the air, in 3D, out of the PLA/ABS plastic used by current fused deposition modelling printers like RepRap and Makerbot.
You can either draw on paper, "peel" off the lines and have a free-standing plastic doodle (or draw sides of a 3D model, peel them off the paper and stick them together), or draw the whole model in freeform from the ground up. The plastic solidifies really fast and supports itself (more or less; you'll still need scaffolding for the more extravagant designs), so you can pretty much just start drawing and it stays up.
Some images:
Doodled on paper and peeled off.
Stencil. Trace the stencil, peel off, assemble.
The prototype. Kinda chunky but
But wait, there's more! Since this is a device that oozes molten plastic, in addition to drawing 3D wangs and signing your name on things in something more impressive than marker, you can also use it to fix stuff, stick stuff to other stuff, and fill cracks, if that's your thing.
Anyway, like I said, it's on Kickstarter right now. It has reached the funding goal already, but there's still time to back the project and/or order one. $75 will get you a 3Doodler pen and a bag of colored plastic. Or you can just wait for someone else to snatch the idea and come out with a smaller, lighter and cheaper version.
No word on a launch date yet.
Kickstarter page
Website