I'm playing Pandora through my Garmin 595LM and have about 850 tunes on a memory card in the Garmin to rely on when I don't have signal.
My favorites are the Pine Box Boys, Bob Dylan, Metallica, Zeppelin, Ac/Dc, John Prine, Leon Russell, Clapton, Beatles, Deep Purple, Black Crows, Counting Crows, (guess I like crows :-) ) The Winters, both Johnny and Edgar, Tool, Steppin' Wolf, Hendrix, Procol Harum, The Spoon Lady, Joe Walsh, The Allman Brothers Band, The Big Damn Band. After that, the list diversifys quite a bit. Once the Classic Rock starts flowing, only the cruise control stands between me and "fast driving awards".