One of my favourites is Avatar and twilight saga movies.. New moon is my favourite right now of twilight saga movies
Rrrrgh... completely off topic but I wish some one would change the title of this thread. I hate the topic title. "YOUR best film ever" I mean come on! Every time I see it I cringe. Can some one please just change it to "Your favorite film of all time" or something normal? I'm sure not everyone here is a film maker. Also I saw a cool movie today called "Lo." It's not one of my favorite I guess in the OP's terms "best" films ever, but it was pretty interesting and I would recommend it if any one is looking to watch a movie that starts off slow but gets better. It's more of a character study, though. So if you're not into that kinda thing.. just make sure you have something else to do while you watch lol.
I have to add Grease too. Really amazing movie, I just saw it again today - seriously, it's old, but it has amazing songs and actors =D
Fight Club is a great movie, the crudeness as well as the ending keep you on the edge of your seat. Also, Ocean's Eleven is superb too.
I'd say one of my definite personal favorites is Amelie. It's just such a sweet quirky romance and Audrey Tautou is really adorable as Amelie. Another, which surprised me as I really don't like Leonardo DiCaprio, was Shutter Island. It seems like a lot of movies with twists are very predictable but that one really took me by surprise.