Shaun of the dead.
Has a strong Dude where's my car quality to it. Can't say I get the point. It was funny like 3 times, otherwise I've no idea where the hell this is going. It's actually remarkably much like another Brit movie about zombies I saw a few months ago, don't recall the name of it. That one wasn't a "comedy" though.
It's a nice movie, fairly harmless, but I didn't find it that funny. It works better as a zombie movie and as a romance. Still, some fun moments: Shaun's walk to the shop and back in the morning, the iterative planning involving killing his father in law and so on.
Hot Fuzz was much funnier for me. Serious parody of cop films (in particular Michael Bay's), and fairly manic at times. It's a hair long, but it's an excellent British comedy.
Spaced, the TV series they did, is seriously nuts by all accounts; I keep meaning to borrow it off someone.