Good songs to have stuck in your head:

"Hooray for Hollywood"

Tonight Show Theme (Johnny Carson version)

Alien Ant Farm - "Smooth Criminal"

Bad songs to have stuck in your head:

Cindi Lauper - "She Bop"

I forget the name of the 80's hair band - "Sister Christian"

Any Carpenters' song

Incidentally, a therapist once told me that it is abnormal to always have a song or other thing in your head. If that's the case, I know a lot of abnormal people. Including me, of course. I've almost always got an inner monologue or song going.