I love this! The start of a never-ending discussion, for sure.

A few of my favorites that you didn't mention:

Ride the High Country. This early Sam Peckinpah film features great performances by Randolph Scott and the much under-rated Joel McCrae as aging gunmen, former friends now on opposite sides of the law.

The Tin Star, features Henry Fonda as the mentor to a young and inexperienced sheriff, played by Anthony Perkins. There's a great performance from Neville Brand as the loud-mouthed bad man.

I'm also partial to Kevin Costner's Open Range, certainly flawed, but featuring one of the best gun fights in western movie history.

And, of course, there is Tombstone, worth watching for Val Kilmer's Doc Holiday.

Thanks!