Maps, for me! (Sometimes Radio, if I'm playing MY Cd's or using the card-reader.)
I like the maps, because sometimes I forget to make this ONE turn on my commute

(Hard to believe I STILL do this at least at few times a year, with the same commute for 5 years.)
If I happen to look at the screen shortly after this brain-disconnect, I'll notice I'm heading Southwest instead of West. I then correct this grievous error more quickly than if I just happen to notice "Hey, that desert isn't on my way to work!"