Anyone mention Undeclared? Because it was just an amazing comedy. I remember when it came out the same year I started College. It's done by the same folks behind Superbad and Freaks and Geeks ect..ect.. And you'll see a lot of the same faces too plus a few more famous faces. In the first episode you'll see the dude who plays Superman in "Smallville" and Pam from the "Office".
The link will take you to a few episodes to try it out.
Very Very underrated.
EDITED: I just noticed Martin had mentioned it but i thought i'd throw it out there again anyways.

Also a few cartoons which I would KILL for the chance to see new episodes:
Clone High: Written by the creator of Scrubs. A bunch of clones of famous people try growing up in a high school. It's one of the funniest shows I have ever seen.
Undergrads: Another great cartoon that I personally love because it reminds me of my friends. Nerd humor galore.

Yeah, Undeclared by the Apatow group is great especially Seth Rogen. I notced the English guy's accent in it is stronger than usual.

Why does this happen though, you know, when English people are in American TV shows or films?

I've always noticed that, and also always wondered why. But I also used to watch Neighbours, but accents weren't really noticeable until I saw them as guests on shows here. So I reckon it's the setting in which they are in. The contrast. And it could also be that they're asked by the director to posh it up. Or both factors.

Perhaps it's something they learned in acting school?