There's (sadly) a lot that I haven't seen, but I'll just keep it to the ones that are routinely brought up as absolute classics:
5) Vertigo
4) Seven Samurai
3) Lawrence Of Arabia
2) The 400 Blows (and all of French New Wave for that matter)
1) All The Presidents Men
And for a slightly different list, the 5 dvds I own that I'm ashamed I've not seen yet
5) The Good, The Bad & The Ugly
4) Anything by Almodovar (I own about 6 or 7 of his films)
3) 8 1/2
2) Chinatown
1) The Godfather Trilogy
Edit: Have since seen ones with a strike.