You may have seen this on MacNN or MacOS Rumors- but since it's such a good cause, we feel it's worth mentioning again...
FlashingYellow is holding a DivX plug-in programming contest for DivX playback. Winner gets $5000 and a Apple iMac DV Special Edition.
In case you've missed it (see DivX on the Rise), DivX is a basically a hacked codec that's been available for windows. It's a hack that merges MPEG4 and MP3 into a high quality/high compression video format. No Mac version currently exists.