To the ones already mentioned, I’d to add:
The Professionals with Lee Marvin, Burt Lancaster, Jack Palance, etc.
Bite the Bullet about a grueling cross-country horse race, with Gene Hackman and James Coburn.
I guess I like end-of-an-era movies; both those take place early in the 20th century.
John Wayne:
McClintock Funny, good natured.
Fort Apache If a frontier cavalry fort didn’t look like this, it should have.
The Man Who Shot Liberty Valance
The Cowboys A rare chance to see Bruce Dern playing a psychotic low-life. (Okay, that’s not so rare.) But a really entertaining movie, with good performances by young actors, and one of Wayne’s most sympathetic roles. (No matter how much I disagree with his political views – which were mainstream conservative for their time – I can’t help liking the guy.)
The Shootist Wayne’s last movie, and one of Wayne’s best performances. Also has Lauren Bacall, James Stewart, Richard Boone and a young Ron Howard.
Jimmy Stewart:
How the West Was Won; actually this has everybody in it. Big, sprawling epic, great soundtrack.
The Naked Spur Jimmy Stewart is tough as nails in this, and it’s a good psychological story.
Early frontier movies:
Jeremiah Johnson Great movie about surviving and making a home in the wilderness. Robert Redford, and Will Geer. (In one scene Will Geer, laughing like a lunatic, lets a bear chase him right into the cabin, which is a big surprise for Robert Redford. Geer says, “You skin this one, pilgrim, and I’ll go get another!”)
The Mountain Men with Charleton Heston and Brian Keith. Got bad reviews, not many people saw it, but I always liked this movie. Beautiful scenery, plenty of action.
A comedy that hasn’t been mentioned: The Frisco Kid, with Gene Wilder and Harrison Ford.
And of course High Noon.