I'm so glad to see The Ox-Bow Incident mentioned. I love it.

My top ten:

1 - Once Upon a Time in the West (1968) 
2 - The Searchers (1956)
3 - The Ox-Bow Incident (1943)
4 - The Man Who Shot Liberty Valance (1962)
5 - The Good, The Bad, and The Ugly (1966)
6 - High Noon (1952)
7 - Unforgiven (1992)
8 - The Shootist (1976)
9 - Rio Bravo (1959)
10 - The Gunfighter (1950)