There are a ton of good westerns on Prime right now.

Hang 'Em High
The Good, the Bad and the Ugly
Hondo
Big Jake
True Grit
Quigley Down Under
Once Upon A Time in the West
Rio Grande
My Name Is Nobody
Gunfight at the O.K. Corral
El Dorado
High Noon
Goin' South
Little Big Man
The Shootist
Stagecoach
Hannie Caulder
The Fighting Kentuckian
Cowboy
Arrowhead
McLintock!