As I was just reminded of it in another thread, I thought I should share with you Triumph the Insult Comic Dog from the Conan O'Brian Show.
I don't know how popular / well-known he really is in America, but if you don't know them, you really should watch these hilarious videos:

At the Star Wars premiere
At the Tony Awards
At the Michael Jackson Trial
At Hollywood Squares

There's much more, but if you aren't addicted after these, you had your sense of humour amputated....

EDIT: Fuck, I messed up the title. If one of the Mods would be so kind...
EDIT2: Thank you.

 

It's the same guy that does the "TV Funhouse" cartoons on Saturday Night Live. Some pretty witty jabs mixed in with a lot of "nerd" jokes on the Star Wars one. I'll watch the rest eventually, but good look there.