MPlayer is a very well known media player, now in an updated version for Windows Mobile.

Changes:

1. Single build for ARMv5/IWMMXT and ARMV6 optimization
2. ARMV6 Optimization.
3. Runtime CPU detection.
4. Skin Support for QVGA,VGA,WVGA,WQVGA and SQVGA with landscape and portrait mode.
5. Continuous play with repeat and shuffle mode
6. Headset Button will change track if MPlayer-GUI is active.
7. Better log visibility.
8. Auto Screen off when audio-only file played.
9. Auto Shutdown
10. GSGetFile is used to open File(s)

http://forum.xda-developers.com/showthread.php?t=520150