VLC: Multimedia Player, Server and Framework [Top 10 Mac Apps for Windows Switchers]

VLC, (Video Lan Client) is an open source audio/video client for Linux, Windows, and Mac OS X.  It's probably the most handy piece of software that you can get, as it has built-in support for pretty much any file you throw at it.  Here's a list of supported codecs.

Download VLC Here

Advanced features of this app include playback of damaged files, DVD, and  TV card,.  It will also encode audio/video, and act as a streaming server. 

For such an outstanding piece of software, you'd expect a hefty price, but this app is 100% Open Source, and FREE.  This project is in need of Mac OS X developers to continue supporting OS X.  If you are a dev, and would like to improve VLC, check out their site for sources and information.

More: Top 10 Mac Apps for Windows Switchers