Finally got the last codec I needed on my Mac Mini to be able to play back any video file I have found thus far, and figured others might have a use for this. My goal was to get Quicktime specifically to play these, as that also means they can be imported into any iMovie/iDVD project. This should have the ability to allow iTunes to play back these as well, along with Front Row on the new iMacs. If you don't have a huge need to edit or play back via Front Row, then using an alternative player like MPlayer or VLC works too.

Anyhow:
Divx 6: http://www.divx.com/divx/mac/download/
XVid delegate: http://people.ee.ethz.ch/~naegelic/download/
3vix: http://www.3ivx.com/download/macos.html
AC3/A52 decoder: http://sourceforge.net/project/showfiles.php?group_id=83360
WMV Decoder for Quicktime, commercial, $10: http://www.flip4mac.com/wmv.htm
Quicktime MPEG2 decoder, $20: http://www.apple.com/quicktime/mpeg2/

If someone comes across a video this can't play back, I'd be interested in getting a copy to then try and get it working.