newbie here, i've used a pocket pc for about 2 months now. i've tried several freeware, but i've kept the following:
GSFinder - to replace the built in file explorer;
GSPlayer - to replace Windows Media Player;
BetaPlayer - can play both music and video; and
the free versions of MobiPocket and Ereader.
special mention also to Calendar+ (though i replaced it with PocketBreeze).