Having been reminded elsewhere by thr0b of the goodness of The Fast Show, I present my favourite sketch from that, and its inexplicable American Werewolf In London qualities.
The Fast Show (in its first two series in particular) really was one of the best sketch shows of all time. The first series was often offbeat and weird, characters that came from nowhere and were never used again. The whole team gelled, and it was a great mixture of comedians and actors.
Even the presence of Arabella Fucking Weir didn't ruin it. Though when Caroline Aherne went, the rot set in.
Also had at least two good spin-offs; namely the sublime Ted & Ralph, which won a ton of awards and hasn't been repeated in years, and Swiss Toni. Which was in itself a spin-off of a character nicked from The Smell Of Reeves & Mortimer, but was a really good fleshing-out of a one-joke sketch into a full length series. Dumped when BBC Three became all chavvy, obv, in favour of series 86 of Two Pints Of Shit And A Packet Of Shit.