The Princess Bride - and if it doesn't hit the top 5, I have only one word to say: "INCONCEIVABLE!"
Planes, Trains, and Automobiles - fits the Thanksgiving/holiday season, and although I don't swear myself (outside my story, that is), Steve Martin's use of like twenty F-bombs in under five minutes is classic and hilarious!
Spaceballs - need I say more?
Robin Hood: Men in Tights - again, no explanation needed. Dancing merry men in tights abound.
The Matrix - the first (and best, imo) in the trilogy
Tremors - classic monster movie that's more funny than scary. Kevin Bacon and Fred Ward play off each other perfectly
Die Hard - one of the best action movies of all time