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.
MPlayer has very good postprocessing. On every image in the movie is applied a filter to reduce square areas, which comes from codec's compression algorithm.