My wife wanted a small MP3 player for running, but getting one compatible with OS X is a big problem. Many players simply ignore the Mac, and those that don't seem to only support OS 9 at best. However we eventually found the Creative MuVo
. It's USP [robg: Unique Selling Proposition?]
is that it's an MP3 player and a storage class USB flash drive (so even if you don't use it as a player...). Although designed to be loaded via Windows Explorer, you can load files by dragging them from an iTunes playlist. The MuVo remenbers the playlist order and you're off and running, literally.
But, internally it appears to be DOS formatted so, it won't always accept filenames that are legal in OSX (like use of the "?" character) so you might have to clean up the filenames by editing them in iTunes. It won't tell you have a problem it jus won't load.
[robg adds: You can find a list of "iTunes aware" MP3 players (along with CD burners) on Apple's Playback Compatibility page.]