Hmm....

OggPlay - Quite possibly the finest music player in the world, ever.

TCPMP - The Core media player on Palm OS - could be nice.

A decent chess game with the ability play against other 770 users across the world, not just 20ft away (are you listening, Sony?)

Oh, and if we're sorting a keyboard for this thing, a word processor is a must have, especially given the size of that lovely, lovely screen.