What is there to say that others on my flist haven't said already?
... I suppose I could make a rec of my own: the Yes, Prime Minister episode A Diplomatic Incident, in which he makes a short but memorable appearance to save Britain from a devious
alien French plot. If you haven't time to watch the whole episode, here's where he first shows up, and his other scene is less than a minute later. Oh, and did I mention Christopher Benjamin's playing the French ambassador?
To follow, I'd suggest the Two Ronnies' Colditz sketch.