What kind of music do you like for roadtrips? For me, I've found that sometimes, clear simpler sound is best. I'm probably not describing that well, but there's some highway noise that you don't see in movies about roadtrips that can interfere with songs.
I associate Cake with trips to Yosemite:
English Beat from weekend roadtrips when I was in the army:
Same with Violent Femmes:
Sometimes I go further back:
Good bass lines help:
Ok Go Usually does well, too:
Of course, the danger with listening to music on road trips is that you'll be sick of the songs by the time the trip is over.