VLC is excellent, its interface is far better than mPlayer as far as the interface (unless you build your own from the free source--for very advanced users). That said, mPlayer does seem to be better at some audio and video formats., look for

mPlayer
"MPlayer OS X 1.0rc1": MPlayer - The Movie Player

Also, you can expand QuickTime's range of files by installing Perian and Flip4Mac:

Perian: Perian - The swiss-army knife of QuickTime® components

Flip4Mac wmv/wma plugin: Flip4Mac - Digital Media Tools for the Mac