Martin Scrocese will get a nod every decade and I think The Aviator and The Departed are two of his best films so....Also, if Shutter Island is as good as it looks, I'm counting it as another win for him in this decade.
The Coen Brothers get a nod for No, Country for Old Men, O, Brother Where Art Thou (my personal favroite of their's) and I actually liked Intolerable Cruelty a lot. Though I didn't care for Burn After Reading, but most loved it.
Clint Eastwood has had an amazing decade with the masterpieces of Mystic River and Letters from Iwo Jima, as well as slew of good to great films like Gran Torino, Changeling and Flags of our Fathers. The only Eastwood film I didn't like, is of course the won he won the Oscar for this year (Million Dollar Baby).
-Alfonso Curon: Y Tu Mama Tambien and Children of Men. 'Nuff said.
-Paul Thomas Anderson: Sure, There Will Be Blood may be his only film thsi decade. But it was that bloody good. Indeed.
up-and-coming directors from the decade there are several of great note:
-Peter Jackson. Yes he did really only three films (I count LOTR as one here) and all of them were CGI-laden, but he proved they can still be great movies under that circumstance.
-Christopher Nolan. Memento is a masterpiece. Insomnia, Batman Begins and The Prestige were all great films. And then The Dark Knight is probably the best blockbuster of the decade and an instant classic. He is going places.
-Edgar Wright: Shaun of the Dead and Hot Fuzz are two of the funniest movies of the decade and show the talent of an auteur just coming into his full range. I expect a lot more from him in the future in terms of classic comedy.
-Jason Reitman: A breath of fresh air in Hollywood. Thank You, For Smoking is one of the most clever films in recent memory and Juno was a heart-warming family film that was poignant and honest as opposed to schmulzy and contrived. Up In The Air looks to be another great film from him.
-Joe Wright: Pride & Prejudice was excellent, Atonement was great and haunting and The Soloist...well he has a lot of room to grow.
And then directors who had a great film this decade, though not as many otherwise deserve mentioning. Baz Luhrman for the masterpiece that is Moulin Rouge; Tim Burton for Sweeney Todd (and Big Fish was quite good too); Speilberg, though not at his best had several really good movies this decade (Minority Report, Catch Me if You Can and his best this time around, Munich); Del Toro gave us Pan's Labyrinth; Ridley Scott for Gladiator (and all his other movies were quite good, but not great from this decade); Ron Howard for A Beautiful Mind; Quentin Tarantino for Inglourious Basterds and to a much lesser degree, Kill Bill; whoever made The Assassination of Jesse James (sorry his name escapes me right now); and there are many others I am sure.