The MP3 Disks
I've been experimenting with MP3 disks (and WMA disks, too.) The Monsoon sound system plays them both.
I got the single-disk Monsoon. I've had some problems with multi-disks in the past (just one more thing to break).
I can say this: With a single disk, and MP3s sampled at 128 (don't need any better than that for the acoustics of top-down driving) I'm fitting a hundred songs on a single disk. That's hours and hours of music.
The display is nice, too. If you scan a disk to load in the folder names (that takes a couple of minutes, but worth it for a long trip) then you can see the folders and navigate to them, as well as see the song titles when they play. Separating your music into "mood" folders works great. And you have a "random" button to mix it up.
Now that I am buringing MP3 disks, I will never carry an official CD in my car again; I will take a collection of albums (or only the tracks that I like) and combine a bunch of them onto a single disk - perfect for my single disk player.