looking for simple drawing program

[notwist]

I've been given the task of writing the lecture notes for this class this semester and have been looking for some free software that will help me draw basic block diagrams. I'm not sure exactly what program I'm looking for but I know it's nothing too complicated or flashy. Anyone have any suggestions?

[lil'homunculus]

http://forums.macrumors.com/showthread.php?t=328253
http://plasq.com/skitch/
http://paintbrush.sourceforge.net/
http://seashore.sourceforge.net/download.php
-also: osxvoodoo, google sketchup, sketchbox and flysketch.