1. Singin' In the Rain (1952) - Stanley Donen and Gene Kelly
2. A Generation (1954), Kanal (1957), Ashes and Diamonds (1958) - Andrzej Wajda
3. The Searchers (1956) - John Ford 
4. On the Waterfront (1954) - Elia Kazan
5. Ben-Hur (1959) - William Wyler 
6. Seventh Seal (1957) - Ingmar Bergman
7. Ace in the Hole (1951) - Billy Wilder
8. East of Eden (1955) - Elia Kazan
9. Paths of Glory (1957) - Stanley Kubrick
10. Invasion of the Body Snatchers (1956) - Donald Speigel

Numbering sucked on this as did all the films I left out, but that's why I had that separate thread, so that I wouldn't leave films out. Although Kazan is the only director with two films, Wilder and Bergman certainly had equally good films that decade, and I realize that my inclusion of Wajda's trilogy might be cheating to some, but I'll probably never separate those films. If forced at gunpoint though I suppose I'd pick Kanal.