Car, minidisc
.
But yeah, that's another reason why I have so many mp3's myself.
I put them on my mp3 player that I hook up to my car stereo. Or I make mixed tapes, which is really easy when the stuff is already on the PC.
Mp3 is really very convenient, but my ears are a bit too good (read: trained by upgrading my audio rig all the time) to be satisfied with mp3 as my only music source.