Not a comedian, but a 16-year-old Kelly Brook plays a schoolgirl that Stewart Lee leches on in Fist of Fun.
Isn't that thingy? Page 4
I watched the episode of Only Fools where Roy Slater nicks Del for stealing a microwave oven this morning.
There's this dopey young PC in the police station in a couple of scenes and I suddenly recognised his dopey voice from somewhere.
It's Gunner Parkin from It Ain't Half Hot Mum.
Anyway I Googled the guy and he died aged 53 of cancer...
Lovely shoulders, show em' off lad! 
"Now Show" regular, Jon Holmes is in the first episode of "Green Wing" as a car salesman trying to sell a car to Joanna Clore.
Alan Patridge has quite a few. Simon Pegg (obviously), Rob Brydon, Kevin Eldon, Steve Brody, Peter Serafinowicz and Hugh Parker (who played the photographer in the Comic Relief ep of The Office)
Spaced had Tony Way (who was the chef in the Ross Kemp ep of Extras), Paul Kaye, David Walliams, Paul Putner, Kevin Eldon, Mark Gattiss, Martin Trenaman
Also, The Office had Tom Goodman-Hill of Ideal fame and Gareth Tunley (who plays Gog in Peep Show) has a brief look at the camera.
Sorry guys... I couldn't resist reeling those off...
Frankie Boyle appeared in Up The Elephant And Round The Castle as Jim Davidson's racist Scottish glue sniffing nephew if memory serves me right. 
Quote: Aaron @ May 1 2011, 8:00 PM BSTMark Steel was also in The Detectives fairly frequently.
He was also in Red Dwarf as a skier in the Timeslides episode.
Rob Brydon appeared in Little Britian.
Just realised that Peter Slater (Alan - Ideal) was in That Peter Kay Thing
Vic Mackey in Seinfeld
Bishop Len Brennan (Father Ted) just popped up on Colditz on Yesterday!
I've been watching Alexei Sayle's Stuff on DVD and one of the regular actors on the show was a youthful 'Lynn' off Alan Partridge!
Apparently Morwenna Banks was in an episode of The Lenny Henry Show. And Caroline Quentin was in an episode of some obscure police cadets drama called The Squad.
Morwenna was also in Alexi Sayle's Stuff!
Kate Winslet was in Get Back.
Paul Merton is in The Young Ones