Will, I use JetAudio and it plays anything you can throw at it, not just audio. I use it for playing DVDs, Films, Audio CDs and even watching the news on the BBC website.
For example if you double click on an avi file it will automatically open and play. It does need to be set up to play Real Player (ra, ram) files but that is easy to do. Once it is installed, open it and go to Preferences, File Type Association, click on Check All and then Update and OK. It should now play anything (audio or video).