Very very good question - so many I can't choose, but here are some that will always stick in my mind
Nelson Mandela's release
The Berlin Wall coming down
Live Aid - Give us your **** Money blurt by Bob
The (Rod Hull and) Emu incident with Billy Connolly, on the Parkinson show
The aforementioned Dell-Boy bar counter scene
The rat in the biscuit tin -Fawlty Towers
Fork Handles - The Two Ronnies
Morcambe and Wise - running out of stairs, during the big musical number
The Young ones - Neil crying because the lentils had blown up
The finale of Blake's Seven