I currently own a presettlement 30g Zen vision M, My major complaints are that I can't load it from my ancient versions of linux and the battery feels like it's always dead. I think it either has some horrible power leak when it's off, or it's pretending to shut off and not actually doing so. It's about the size of deck of playing cards and the UI is acceptable.
So here are my top contenders:
Creative X-fi. Price: $250
cowon d2 16g + 16g SD card, price: $144 + $30