It's Always Sunny In Philadelphia - This is one of the funniest things that's been on television in a long time and it's a real shame it has more or less no airtime in the UK.
Also, why are Robot Chicken and Pasila the only animated comedies to feature yet? I like a lot of what's been listed but just to gives props to cartoons...
The Simpsons
Futurama
Frisky Dingo
Archer
South Park
Family Guy
American Dad
And then a whole load more kid's cartoons like 2 Stupid Dogs, Earthworm Jim, Johnny Bravo, Cat Dog, Oggy and The Cockroaches.