Okay, Shawn of the Dead, Hot Fuzz, blah blah blah. But for my money, Simon Pegg's greatest ever moment came during the Brass Eye Special when the presenters are united in a terrible singalong (led by "the St Lazurus The Amethyst School Choir") encapsulating the lessons learnt during the programme.
Pegg only appears for several seconds, as the guitarist, but steals the show, despite not even being in the foreground of the shot. Sporting a wig of long curly blond hair and a white Mojo readers muso shirt, he combines ostentatious gum-chewing and a show-off guitar fill to make the programme's funniest moment. It's at 7.40 on the vid below (or 2.20 if it's showing time remaining).