In terms of software available for the Mac on playing back media files there are:
VLC (Video LAN Client)
mPlayer (of the Linux fame)
Quicktime Movie Player (will handle MPEG-2 file if you throw $20 at it...yeah, I find that absurd too)
Windows Media Player 9 (sucks, does not handle DRM encoded files properly if at all)
Between all these choices there is something to suit everyone I believe. I just downloaded the mPlayer on Friday and found it to be MUCH better than a version I used about a year ago (DUH!)
In terms of audio, there is:
iTunes, and a million and one ways to talk to it (various scripts and frontends).
Audion (which is now free and supports skinning as iTunes does not and likely will never).
Winamp for Mac (which I THINK is Audion anyways?)
for TV stuff there is the Eyegato setup which is an MPEG-2 USB 2 setup for watching and PVR for TV
There is probably more, but I am late in picking up my GF

...so later!