Eric Millikin (Fetus-X) has an ambitious twist on Scott McCloud's 24 Hour Comic Challenge.

There's more discussion on this thread at Talkaboutcomics but here's the basic idea:

I think a coool idea would be a 24-hour jam comic, with 24 artists. Each artist gets an hour to do a page, then they hand off to the next artist, so that in the end of 24 hours there are *24* 24-page, 24-hour comics, each comic having one page from each artist.

Maybe the best way to do it would be online, where each artist has an hour to post a page to a web site. Might make for an interesting Modern Tales Longplay, updated in real time for all the world to see ...