The breaching killer whales of South America, which first appeared in The Trials of Life and later in The Blue Planet.
Two words: Planet Earth.
2016's sequel, Planet Earth II, is equally impressive. The scene where a baby marine iguana makes a miraculous escape from a swarm of racer snakes has received critical acclaim due to its cinematic feel.
The infamous scene of the baby seal walking along a beach; only to be eaten by a breaching killer whale. The scene was entirely unintentional and possibly one of the greatest shots from any documentary ever produced.
The Lyre Bird. There's a reason it has over 14 million hits as of 2015, and counting.
The episode which showed the exploration of underwater caves. Specifically the moment when the diver tried to squeeze through the narrow gap. Claustrophobia mixed with the fear of damaging the life-support equipment to the max.
Any time wasps show up in Life in the Undergrowth, you learn facts about those things you'll wish you never did. By the end of that series the word "wasp" will trigger a Pavlovian cringe response.
The great white shark attack from Planet Earth, and the lion pride which successfully bring down a baby elephant at night.
The racer snake attack from Planet Earth II.
Values Dissonance: Acknowledges in Life on Camera that keeping a "pet" ape and eating raw sea turtle eggs isn't as funny in The New Tens as it was in the Fifties.