Rule: There has to be at least 3 films currently in existence to deserve qualification to this thread.
My choice favourites (a little bit mainstream perhaps):
Lord Of The Rings - I can just put this on whenever really and enjoy it as much as I did when I saw them at the cinema
The Dark Knight Trilogy - The other two are good films, but this is mostly due to The Dark Knight being so great.
Back To The Future - Quite consistent good fun.
The prequel trilogy stops me including star wars. So go on, what's yours? (I imagine you'll all pick something super cool/indie and I'll lose all indie points here).