The Holy Grail is my favorite. However; I love the Life of Brian simply because it was hilarious, especially with all of the fanatics outside the theatre protesting it and saying how blasphemous it was. We ended up talking to some of the protesters and found out they never even saw the movie. Then of course the Meaning of Life.
There is one that is an off the path, kind of Monty Python show I liked. "All You Need is Cash" featuring the Rutles. Great spoof on the Beatles with George Harrison producing it and having a cameo in it. One of my students actually printed out the entire script to the Holy Grail and gave it to me.