Another one designed specifically for driving, but it's simpler (less options on the settings, apparently) than others. FluxTunes.

FlexTunes is a lifesaver, maybe literally, when you’re on the freeway and can’t take the time to look at the iPod screen to change songs.

- Tap to pause/restart
– Slide left and right to change tracks
– Slide up and down to adjust volume
– Slide two fingers left or right to change playlists
– Slide two fingers up to play music from your whole library
– Slide two fingers down to select playlists/albums/songs