[lm741]

I built an Ultimaker last year. Having the ability to go from an idea to a physical widget on a weekend afternoon is amazing.

Here's a working turbine compressor model that I built http://www.youtube.com/watch?v=rjU-1aS_mHQ

Here's one of the more practical things that I made: http://www.heroicrobotics.com/img/pixelpusher_case.jpg (We used another "consumer grade" 3d printer for the first 60 units; it's about time to switch to injection molding)