I will be the first to mention Robert Zemeckis, along with Clint Eastwood, Steven Spielberg, Martin Scorsese, Quentin Tarantino, and Joel and Ethan Cohen.
To reach ten, I will need to contemplate some others. I am not counting Francis Ford Coppola simply because I am considering directors actively making an impact today.

1. Terrence Malick
2. Martin Scorsese
3. David Lynch
4. Paul Thomas Anderson
5. Francis Ford Coppola
6. Darren Aronofsky
7. Wes Anderson
8. David Fincher
9. Coen brothers
10. Sofia Coppola

This is a discussion about Top 10 AMERICAN directors. Not directors in general.

What about Jean-Luc Godard

So you call Kevin Smith a good director and the Coens overrated ? Smith is a fine writer, but a terrible director.

1 Scorsese - since the mid 70's consistently the best
2 P T Anderson - still quite young and has already made several great films and an excellent writer
3 Coen brothers - equally capable of handling different genres, yet all their films feel distinctive
4 Fincher - Visually great, and a brilliant storyteller
5 Allen - Recent worb68k has been hit and miss (and miss) but made alot of good pictures in the late 70's and throughout the 80's. Demonstrated he still has 'it' with Match Point
6 Aronofsky - Inventive and exciting director
7 Malick - small volume of output however he always makes good to great films
8 Wes Anderson - possesses a unique and consistent visual style
9 Lynch - A true artist
10 Francis Ford Coppola - Great during the 70's also made interesting films outside that period (Rumble Fish)
If I could add and eleventh it would be Tarantino or Gus Van Sant
You don't make up for your sins in the church, you do it on the streets.

hang on to your ego

In alphabetical order:
Woody Allen
P.T. Anderson
Tim Burton
The Coen Brothers (except their comedies)
Julian Schnabel
Steven Spielberg
and thats all! There is no Top 10.
There are some who are still alive, used to be interesting but are not interesting anymore: Scorsese, Lynch, Tarantino and Jim Jarmusch.

Nolan and Scott are British, Forman is Czech.

Chris Nolan
Wes Anderson
Darren Aronofsky
Milos Forman
Francis Ford Coppola
Martin Scorsese
Steven Spielberg
Ridley Scott
Paul Thomas Anderson
The Coen Brothers
Fidelio

Coen overratedwhat about Tarantino??????????

Cronenberg is incredibly underrated and would totally go as number 1 in my lost of top directors, but as this is for American Directors and he is, in fact, Canadian, he doesn't really fit.

Hmm. I agree on Van Sant. He is going to be remembered as one of the great directors of his time. In addition to Van Sant, I would also add the Cohens, Eastwood, and Cronenburg to my top 4. I like Wes Anderson but he just does do it fo me like these other guys.
I think Sophia Coppola might make this list eventually.

i guess im the only person who would put wes anderson as the best director today..gus van sant and cameron crowe follow closely

Spielberg is a good producer mediocre director, tarantino a great writer as a director eh, and Lucas is awful as is spike lee. I agree that stone is overrated and coen bros are a lot better than you are giving them credit for

In some sort of rough order, my favorite American filmmakers are Jim Jarmusch, Terrence Malick, Gus Van Sant, Darren Aronofsky, Paul Thomas Anderson, Woody Allen, John Sayles, Clint Eastwood, Wes Anderson, and the Coen Brothers. I would definitely consider Spike Jonze on this list but I'll wait until after Where the Wild Things Are has been released. Also, to put Ron Howard, George Lucas, and Kevin Smith on your list is questionable, and Spielberg only makes a good movie every 5 years or so, and Frank Darabont has only made one great film and a lot of mediocre ones.