I haven't seen enough movies to really make a list, but we really do need to do this with music on Prefix too. I believe Nick N. suggested that.

 (1) Excellence when it came out; (2) Rewatchability; (3) Originality. Connelly proposed the corollary that the "defining" film must be loved, not simply admired. (Goodfellas and The Shawshank Redemption were deemed two exemplary examples from the 1990s).

 

....

5. The 40 Year-Old Virgin  - Steve Carell's field-trip to Planned Parenthood.
4. Almost Famous - Any scene with Philip Seymour Hoffman's so-not-cool-he's-cool Lester Bangs
3. Cast Away - Tom Hanks' painful reunion with Helen Hunt.
2. Michael Clayton - The moment you learn why the GPS in George Clooney's car isn't working.
1. The Dark Knight - Heath Ledger's police station interrogation with Gary Oldman and Christian Bale.

http://popwatch.ew.com/popwatch/2009/07/movie-of-the-decade.html?xid=rss-feed-todayslatest-Film+of+the+decade%3A+Your+pick%3F

I'd nominate Closer because of the excellent role by that whore Natalie Portman basically playing a whore. Oh Snap, I just took it there!!!

I did really enjoy that movie though.