Well @#%$ this already got deleted once. I'll play along with your rules by selecting just one per director, but I'm going to break mine down foreign and domestic.

Foreign
1. Berlin Alexanderplatz - Fassbinder
2. Landscape in the Mist - Angelopoulus
3. Ran - Kurosawa
4. Wings of Desire - Wenders
5. Fanny and Alexander - Bergman
6. Cobra Verde - Herzog
7. The Decalogue - Kieslowski
8. The Cyclist - Makhmalbaf
9. Akira - Otomo
10. Shoah - Lanzmann

Domestic
1. Ordinary People - Redford
2. Raging Bull - Scorsese
3. The Shining - Kubrick
4. A Christmas Story - Clark
5. Pink Floyd's The Wall - Parker
6. Airplane - Zucker, Abraham, Zucker
7. Platoon - Stone
8. Do the Right Thing - Lee
9. Raising Arizona - Coen
10. The Princess Bride - Reiner

Lots of @#%$ I wish I could have put on. Videodrome was a tough choice to exclude, as was Predator, Die Hard, Last Temptation of Christ, Paris Texas, Nostalghia, Salvador, Drowning by Numbers, Pee-Wee's Big Adventure, and Who Framed Roger Rabit? among many others.