Ziggy Stardust said:

2011: Source Code

2010: True Grit

2009: Moon

2008: Wall-e

2007:

2006

2005: Munich

Black Swan >>>>> True Grit

2005 Should go to A History of Violence

Some contenders for 06 & 07 to help you choose:

2006:
Pan's Labyrinth
The Prestige
Children of Men
Little Miss Sunshine
Borat
The Proposition
The Departed

2007:
There Will Be Blood
No Country for Old Men
Sunshine
Before the Devil Knows You're Dead
Atonement
3:10 to Yuma
Michael Clayton
The Diving Bell & The Butterfly
The Orphanage
Into the Wild
Sicko