My favorite project is my RepRap Prusa V2 Rapid Prototype machine.
It is very reliable, and allows me to imagine, draw, and make very quickly.
Many of my other projects rely heavily on this machine.
How it Works:
This machine works by precisely depositing molten plastic, layer by layer, on a heated glass bed.
My workflow is typically as follows:
-Download from Thingiverse.com
-Create manually with Sketchup or Autodesk 123design
-Slice with Repetier Host and Slic3r
Load into 3D Printer and Print
-I use an SD card