Boing boing posted a link to this list of the "The 50 greatest comedy sketches of all time" that was put out by IFC. It's not worth arguing over the order of their rankings or what was and was not included on the list at all. They put together one hell of a list. There are tons of classics on here (Dead Parrot, Land Shark, Who's On First?) and plenty that I had never seen before. I recommend tackling this list over a couple of days because there is a lot worth seeing.