Favored Freeware: MPlayerOSX

MPlayerOSX is binary distribution of MPlayer (The Movie Player for Linux) and comes with native GUI in MacOSX. After installation you can simply (by Drag&Drop) play almost all 3ivx, DivX 3,4,5 and other codecs files in the window or fullscreen mode. Rendering of very nice antialiased text-based subtitles is also supported.

Pros: Plays almost all movie formats, including DivX.

Cons: Tends to be a bit buggy.