I don't think Billy Joel should be considered a guilty pleasure, honestly. He is kickass, and I actually really like most of all his songs.

Guiltness List:
Cake - Particularly the Frank Sonatra and He's Going The Distance songs...
Maroon 5 - This Love... Shoot me now?
Prince - You Don't Have to be Rich...
Al Green - So In Love With You... BOO YA!

Thats all I can think of at this point, or rather, that I want to disclose...