VLC Player

Just to follow up on the VideoLAN post- I haven't set up any media networks yet, as I have found no immediate need for such a thing. But to watch large-ish video files in formats that Quicktime Player won't handle, VLC is a great choice.  Very smooth playback and good quality sound, with a pretty slick interface.  The only thing is that even when paused, my iBook will not go into sleep mode, while pausing MPlayer will allow sleep.  I've found that in the case of my iBook, which is a few years old and running at 500 Mhz, the VLC player performs better overall than MPlayer, which sometimes gives jittery playback.  I recommend both players because your mileage may vary!