Any of the "Dead Parrot" sketches were good, the entire movie "Life of Brian" was good, but I think my personal favorites are a five way tie between:

1) The opening credits of "Meaning of Life" with song that is behind them.

2) The opening sequence of "Meaning of Life" with the Catholic couple and all the children singing "Every Sperm is Sacred",

3) The end sequence of "Meaning of Life", with the 2 dead couples and their conversation with Death ("The fish was poisoned.")

4) The opening credits of Holy Grail (Ralph the Wonder Llama)...

5) Somewhere in the middle of Holy Grail where the sun, moon, and other heavenly bodies are jumping up and down and the priest goes down about a million stairs to tell them to stop...