VLC is a very solid cross-platform multimedia player which has support for almost every format. The other big crossplatform player is MPlayer. Both being free software.
Of course they run on GNU/Linux too, but there, there are also many other decent players availlable.

What a quick response! Thank you so much for the link. That looks great. I'm downloading it as we speak, and I can't wait to try it.

Thanks again Mauro

Banshee is a very cool music app more similar to iTunes or Realplayer than WMP but does its job really well. From the video point of view though VLC, MPlayer or Xine are all great options which will also play music files :D

Jon

Have you looked at Lsongs? It seems like a good replacement for WMP's music capabilities.

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All three are Linux only.

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Andrew Min