My preliminary list (there are still some strong contenders that I haven't seen yet and the order could still change some) :
1. A Prairie Home Companion
2. United 93
3. Stranger Than Fiction
4. Babel
5. Little Children
6. The Departed
7. Superman Returns
8. The Fountain
9. Inside Man
10. The Proposition
11. Three Times (Zui hao de shi guang)
12. Don't Come Knocking
13. Marie Antoinette
14. A Scanner Darkly
15. Casino Royale
16. Running Scared
17. The Prestige
18. Little Miss Sunshine
19. The Three Burials of Melquiades Estrada
20. Lady in the Water
20. The Science of Sleep
Honorable Mentions: V for Vendetta, Hard Candy, Half Nelson, Hollywoodland, Crank, The Black Dahlia, Caché, Scoop