I think this deserves it's own thread.
It's hard to know, isn't it? For me most of the greatest films of this decade have been pretty small-profile (and foreign) compared to the Avengers shite: Under the Skin, Ida, Force Majeure, the Great Beauty... I don't think that enough people have watched any of those for them to really become classics in a popular sense. The King's Speech is one that is nailed on. I'd argue for Her as well. I guess if you go further back there's There Will Be Blood, or Lost in Translation (though that seems to split opinions pretty well). Skyfall probably will go down as a classic. I love Wes Anderson but I'm not sure he's really made a classic film yet.
I was also barely sentient between 2000 and 2011 or so, so I'm sure to have missed a lot.