Miro

Beautiful interface. Plays any video type (much more than quicktime). Subscribe to video RSS, download, and watch all in one. Torrent support. Search and download from YouTube and others.
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VLC

Plays more video files than most players: Quicktime, AVI, DIVX, OGG, and more. Pretty good interface.
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MPlayer

The interface and buttons are not as nice or as Mac-like in feel, but it may play even more video files than VLC.
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Perian

A plugin that allows quicktime to play additional video formats. (Included in Democracy Player.)
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Handbrake

DVD ripper and MPEG-4 / H.264 encoding. Very simple to use.
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Burn

CD and DVD Burner.
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Centerstage

Full-screen interface for playing audio, video, and photos. Connect it to your TV.
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