I'm liking my new Sandisk Sansa m250. Holds all my music with room to spare, and uses an AAA battery, which means I can change it on the job. The coolest part is the nice and SHORT usb cable that it shipped with - it's about time.
UPDATE: Garrett thinks the equivalent player from Creative Zen is a contender. It sports a bigger screen and photo/video capability, but at nearly twice the price, I think I'll pass. Besides, I can't stand proprietary batteries. And who wants to watch movies on a 1.5 inch screen, anyway? Give me a break.