A while back I was going to post this Escher Photoshop Contest which sounds like it would be a fun project if you were doing a lesson based around the artwork of MC Escher. The work on this page was done in photoshop, but it could be used as examples for other mediums as well (I have a student who did an Escher video this year - he did a great job, I'll try to post it at some point). Anyway, I forgot about it for some reason or another, but then came across this Escher site that has videos that move through Escher paintings, audio interviews with Escher that you could play while the students work, and of course, a gallery of his work.

So then I figured, why not just find a whole bunch of good Escher stuff?

Check out James Dyson's Escher inspired fountain, then explore this interactive (somewhat) 3D Escher piece.

Finally, Cybermuse has some Escher Resources for you as well.