You could try Media Player Classic and/or VideoLan. MPC is an independent development of Windows Media Player 6.4, VLC is a very capable multimedia player and streaming server. Both to a great extent rely on inbuilt filters/codecs. Small, stable, configurable, and free:
http://www.videohelp.com/tools?s=11#11
Neither one is very flashy, if it matters to you. If you like one better than WMP, just go into options and associate media files with the player. (Assuming WMP hasn't fooked your codecs, etc., and all files play okay in either/both players.) Personally, I'd go into Add/Remove Programs -> Set Program Access and Defaults. Then disable WMP. JMO.
Good luck.
