If you have hawk eyes or simply the desire to do everything small, check out Picard's latest version (http://picard.exceed.hu/tcpmp/test/) of The Core Pocket Media Player (TCPMP) for Pocket PC and Palm OS. Changelog for the past few updates:

version 0.66j:
-language CS updated by Triple T
-WinCE: codepage handling fixes
-WinCE: stereo mode (swapped,join,left,right) fix
-PalmOS: Treo650 exit crash fixed (Treo650 screen blanking feature removed)

version 0.66i:
-language CHS updated by coool
-another mpeg4 problem fix (from 0.66g)
-PalmOS: plugin memory leak fix (from 0.66g)
-Win32: floating point mpeg audio layer1/2 fix (from 0.66g)

version 0.66h:
+PalmOS: Treo650 screen blanking (?)
-mpeg4 artifact fix (from 0.66g)
-fix mp3 silence after seeking (from 0.66g)

Thanks for the heads up Colin. I just checked my version and realised I'm still running 0.66e!!! Shock and horror!!! TCPMP is one app I keep bleeding edge, I must be slacking off... :p

I feel so deprived! I only just discovered TCPMP last week courtesy of the forum contributors on Palm Addict. Amazing! Realtime MP4 decoding on a PDA! And to think that my Powerbook G4 867Mhz still has some difficulty with it!

Evan, I share your joy with TCPMP! Earlier I made some remarks regarding playing MP4+AVC media files:

http://www.mobileread.com/forums/showthread.php?t=4393