Live Action:
Corner Gas - It's only been off of the air for a few years but it's already a Canadian classic.
Seinfeld - Just about every episode is rewatchable, which is good since its re-runs seem to be on every channel.
The Closer - Only recently got into re-runs of this show a little while after it finished but it is good stuff.
Cutthroat Kitchen - Which is a nice spin on the cooking competition format, with chefs going at each other's throats and wallets.
Community - A show worthy of the critical praise it received, minus the first few episodes of season one and most of the fourth season.
The Late Late Show with Craig Ferguson - "Careful, Icarus."
Cartoons:
Animaniacs - One of the finest comedies to incorporate satire, parody, and savvy political commentary into its gags.
Frisky Dingo - From the guys who would eventually bring you Archer (also a great show) comes the story of a giant naked alien and the rich a-hole who tries to stop him.
Clone High - 13 semi-strange/glorious/acquired taste episodes about cloned historical figures.
Spider-Man: The Animated Series - "SHOOOOOOOCKKKKKEEEEEEEER!"
Moral Orel - One of the sweetest, strangest and saddest pieces of claymaytion ever made.
The Simpsons - I know the quality has gone down in recent years but darn it if it's first twelve or so seasons aren't filled to burst with comedy gold.