The best film ever is Il Buono, Il Brutto, Il Cattivo (or, to give it it's english translation, The Good, The Bad and The Ugly). People write it off because it's a western, but this film redifined the genre. It is Leone's masterpiece, a work of cinematographic art (it is the best cinematography i've ever seen, some of the images are stunning), with a soundtrack that complements the images better than in almost any other film (the master Morricone near his best). Added to that three wonderfully textured characters, the performance of Eli Wallach and Lee Van Cleef's lives and one of Clint Eastwood's best as well. If you haven't seen it, watch it, and then change your list.
(other opinions are of course available, but they are of course wrong).