For the penultimate in this series, I will cover the Media Players that I use on MacOSX. (Tim is currently having website problems).
Firstly there is the venerable QuickTime.
Although it certainly is a worthy media player it is held back by QuickTime pro, the version that has all the useful features unlocked. Firstly fullscreen is unavailable in QuickTime- but not in iTunes, both programs based on the same framework. Also much of the functionality can be regained by running applescript. It has support for all major media formats and is easily expandable by use of plugins (such as flipformac).
Next is iTunes. 
By using the same frameworks as QuickTime, iTunes is also able to play any QuickTime file- however when using fullscreen mode there is no OSD. iTunes is primarily used for media management, and copying music and video to the iPod. Oh, it also has a music store.
Although the best way to play media files on any mac is through frontrow, however it is only available on late G5 imacs and intel macs.
Finally two other programs useful for media playing:
EyeTV
Elgato’s EyeTV program is perhaps the only viable DVR solution for OSX. Especially now with its’ full screen menu display and front row integration.
VLC
Videolan is probably the best multi-platform media player, it has the best OSX specific integration, such as growl compatibility and a custom interface. It has good compatibility playing video files. But most importantly- it’s playback window can float on top of the others without hacks.
