A group on Youtube has put together a bunch of rap battles for us to enjoy. The first ep was kind of weak to me (I didn't care much for it) but they get progressively better as they go along (with exception to maybe #4).
Episode 1: John Lennon V Bill O'Reilly
Episode 2: Darth Vader vs Hitler
Episode 3: Abe Lincoln VS Chuck Norris
Episode 4: Sarah Palin VS Lady Gaga