DivX, Xvid, others in iTunes 6
   They don't work. Right? Nope. You'll need Quicktime Pro, but if you do - and have the right QT codecs installed - you can simply save the .avi or .divx files as a referenced .mov file. Sure, it adds a file, but it's small, and 
this file 
can be added to iTunes, where you can also add meta-information etc. Unless you want to view these files on an iPod, you don't even have to reencode the movies.