Kaffeine Is Good
I just wanted to give props to Kaffeine, the KDE-optimized audio/video player. It’s a front-end to xine, a free audio/video engine. Together they play just about any video format that I’ve thrown at them. And Kaffeine does it with style. It’s one of the most satisfying, solid, and stylish open-source programs I’ve used. (See also Firefox.)
Make sure you know how to spell it. It’s German. Not that there’s anything wrong with that.