Again, with Clint Eastwood, I think of acting, not directing. That said, Gran Torino and Million Dollar Baby were some of the best films I've ever seen.
And of course, Scorsese. My husband and I just got back from attending the Turner Classic Movies film festival in LA and Scorsese was a surprise guest. We got to see him introduce the original The Man Who Knew Too Much. It was so awesome to see and hear him in person!
I don't know much about Kathryn Bigelow, though I do think The Hurt Locker and Zero Dark Thirty were both amazing films.
We had an opportunity to see Werner Herzon when he did a presentation of Cave of Forgotten Dreams at ASU a few years ago. He was AMAZING! Also, my husband just got to interview Veronica Ferres (who is in Herzog's film Salt and Fire). I think I've seen him more as an actor than a director. What is it specifically about his work that makes him great?
I've loved everything I've seen by Wes Anderson. I love his quirky view on life and the sense of humor he puts into his films.