I've heard (or used) these:
Elrond: Agent Smith (but I call him Spock)
Boromir: Boron
Aragorn: Argon, that king dude (don't hate me for this one, but one of my friends calls him "balding butt-hole chin")
Denethor: Pyro
Gandalf: Gandy
Sam: Spam ("Bored of the Rings" is an awesome book!)
Eowyn: Eow-not again!
Arwen: Barbie (vacant expression, blue eyes, wait; she must be a Weasley!)
