Needs to be no more than about $50
Needs to have a simple USB hook-up with drag-drop functionality (itunes does not apply here)
Needs to have at least 4gb capacity
Prefer a rechargeable battery
Needs to not completely suck
I'm afraid you are being optimistic -- the only reason Sony are now offering pretty good products without proprietary software (e.g. itunes type annoyances) is that they're corporate pride has been hurt by Apple dominating the portable music sector that used to be Sony's, primarily.
I believe Creative products sound good, but I think there are reliability or support issues. Samsung are also mentioned as good.