It depends on why I'm riding. If I want to be aggressive, then probably some Five Finger Death Punch or Avenged Sevenfold or Dream Theater or Breaking Benjamin.
For just cruising, Joe Satriani (except Surfing With The Alien...THAT goes up above with the aggressive), Rush, Roger Clyne And The Peacemakers, George Thorogood, ZZ Top, Tom Petty.
If I just want to cruise fast but not be overly aggressive, then I throw on some electronica like Orbital or Deadmau5 or Aphex Twin or some Daft Punk or maybe some Oakenfold. RJD2 is good for just cruisin the back roads too.
Sometimes I just throw on a classic rock playlist on shuffle too though. I've got about 10 gigs of just 70's classic rock. I seriously think I was born like 10 years too late. My favorite music to this day is still 70's music.