Early last summer I came across an weird and wonderful article online, written by Andrew Lipson, called "Mathematical LEGO Sculptures". Then some months later the same Lipson was covered in Wired in a short article . So now seems a good time to bring it to your attention - Lego can be used for highly technical illustration, not to mention as the foundation of some fascinating discussions.
"I'm not quite sure how it first occurred to me to build a Möbius band out of LEGO bricks, but the thought was irresistible"
(his personal site has moved since the first article was published, and can now be found at ASL - which also features a wide variety of other Lego works)