Thanks for all the input so far. I guess there is no definitive list of what works.
I currently have a 2nd gen iPod, but I was thinking of upgrading to an iPod Touch when my car arrives, but now I'm not so sure since people have been having problems with a bunch of different mp3 players.
Maybe I'll start with my 250GB USB hard drive
more likely I'll use one of the 16GB flash drives that I have.