The Uruk-hai could sing "We Will Rock You" while banging their spears and such on the ground at Helm's Deep.
At Bilbo's party, when he puts on the Ring, there should be a loud popping noise, like a bubble. (The same with Sauron when he "explodes.")
For those of you who are familiar with albinoblacksheep.com, "
The Llama Song" in the Shire.
Robin Williams as Gandalf, for no reason at all.