Not seen Kill Bill 2 yet, so my vote so far has to go to Eternal Sunshine of the Spotless Mind. Great story, pacing - plus funny and thought-provoking at the same time.
EDIT: I see a lot of folk are voting for Return of The King - I would too, but as it was released mid-December last year, I sort of discounted it! Also, depending on where you're posting from, The Last Samurai could have been last year's film, or this year's. I know it wasn't released here in the UK until after New Year.
Edited, Wed Aug 4 12:25:14 2004 by Kelanthor