VideoLAN - VLC media player - Open Source Multimedia Framework and Player
Good for mac and pc and it is free.
"It plays everything!"
The media player that fills all your needs. It can handle DVDs, (S)VCDs, Audio CDs, web streams, TV cards and much more.
You don't need to keep track of a dozen codec packs you need to have installed. VLC has all codecs built-in. It comes with support for nearly all codec there is.
And what is more it can even play back the file or media if it is damaged! Missing or broken pieces are no stop to VLC, it plays all the video and audio information that's still intact.