While most people will tell you to simply use VideoLan Client to watch the various flavors of DivX movies floating around on the net, there are only so many things you can do with video without having to use QuickTime. I also find QuickTime Player's performance and interface to be far better than that of the other players out there. Luckily, there are two different (free) QuickTime plugins that allow you to use DivX-encoded AVI files within the QuickTime environment. However, both of them have pretty serious flaws.
3ivx D4 will play just about any of the various DivX iterations within QuickTime, but due to a bug in QuickTime, won't play any MP3-encoded audio without a lengthy conversion process (which means double the hard drive space). The new files are not Windows friendly! Too bad a good 80% of DivX files out there use MP3 audio.
DivX for Mac plays DivX 3.11, 4 and 5 files flawlessly, with full audio support (apparently they found a workaround for the QT bug), but will refuse to play any XivD files -- XivD is the open-source DivX spin-off, so the DivX people are understandably trying to quench it. Unfortunately, more and more files these days are XivD.
The solution: just install both! 3ivX's plug-in will take over for all of the video duties, while the DivX plug-in will step in to play MP3 audio tracks. After you have both plug-ins in your ~/Library -> QuickTime folder, almost all DivX-ish files will play, convert, and edit seamlessly.
Perfect! Now we just need Ogg, Matroska and WMA/WM8 support in QuickTime and we'll be all set!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030825045710515