And since others have given multiple answers, I'll throw in Botswana and Vietnam.
(this is rather similar to the "what is your favourite special?" question, is it not?)
I can watch the "Supercars for less than a 2 year old Mondeo" challenge over and over. Also, the trip to Africa or the Vietnam trip are supremely re-watchable.
Polar special (TV or DVD versions), supercars for less than Mondeo both for the parking and Dame Ellen, Sebastian Vettel interview episode, blind man does a lap episode plus Bolivia.