I've probably forgotten about more films than most of ya'll have ever watched. Can't possibly just chose one all-time best. I'll share a few of my favourite films that pop into my mind right now.
Just a few minutes ago I finished watching "District 9", that one definitely earned a spot between my all-time favourites.
The Godfather is a classic, V for Vendetta is great, The Green Hornet is very amusing, The prestige is incredibly written, American History X has a very strong plot, The Matrix (one) is just way too damn good, King Kong (1933) can't ever be forgotten, Jaws (1975) is just great horror, All About Eve (1950) is a classic that only keep becoming better as it ages.
So much for sharing a few of my favourites.