Divx for OS X
Over the past few months, developers have been working to bring Divx to the Mac. If you're unaware... Divx is a Video Codec which provides a high compression ratio - allowing you to compress a full movie down to around 600megs.
The most promising player for X is Divosx... it provides a Quicktime plug-in which provides Divx translation. It's limited to Divx files with MP3 audio tracks. As well, due to bug in Quicktime's AVI handling, Divx files must be preprocessed with an included app (Avi2Mov).
In my own informal testing, it appears to work with the majority of Divx files I've run across. There is still a small percentage which still cause some problems however. Regardless, a vast improvement over other solutions.