These are the only westerns I own (and the majority of what I've seen):
The Good, the Bad, and the Ugly--As I've mentioned, this is the best!
Once Upon a Time in the West--A pretty remarkable film.
The Ox-Bow Incident--Very fine movie.
Unforgiven--Harsh and wonderful.
Django--Good fun!
My Darling Clementine--Excellent, excellent movie!
The Wild Bunch--Not my favorite, but it's a very good film.
The Great Silence--A bleak movie, but worthwhile.
God's Gun/Kid Dynamite (crappy Digiview DVD)--
God's Gun is horrible! But it has some funny bits. I haven't watched
Kid DynamiteHigh Plains Drifter--A bit odd but good.
My Name is Nobody--Not everything in it works, but it's still a great movie.
Rio Bravo (actually, I haven't watched this yet)
Others I've seen that qualify as westerns:
Dances With Wolves--Decent film from what I remember.
Old Yeller--Tragic!
The Terror of Tiny Town--