Pen/Marker Prusa i3 Adapter Mk2:

A nice way to print in 2D with your 3D printer :)
For drawing with this, you'll need to set the temperature off (30ºC) in the gcode, and disable the extruder motor (M103 at the very beginning). Then set it to lift 3mm or so when it does retraction (for not to mess the drawing), then attach a pen to your printer and start drawing!

This is an upgraded version of -> http://www.thingiverse.com/thing:1514064
you can keep it attached all the time, an print with pla and other materials without re