Not enough love for Silverado on this list. Just a wonderful little movie that is kind of full of western cliches, but somehow pulls it off in a very rousing way. In addition, came along in a period where there were very few westerns being made period, and none which were good.
As I was reading through the list I was thinking "What, no-one defending Dances with Wolves?" just a few posts ago. I think a movie that at the time it came out was fantastic, but became weighed down by its own (and Costner's) reputation. Still a fine (if overlong) film.
Never a big fan of the old time westerns, but Rio Bravo was a great one.
Also love with all my heart For a Few Dollars More and The Good, the Bad and the Ugly, but for some reason never thought much of Fistful of Dollars and was not as impressed with Once Upon a Time In the West to the point I never really went farther into Leone's catalog.
(I'd maybe argue in favor of any Clint Eastwood western at all, I'm not sure any of them are bad, though I never thought much of Pale Rider. )
And finally, can't believe no-one has brought up Blazing Saddles...yes a comedy but also a Western, that so accurately skewered the genre as to nearly kill it. (And probably higher up on my list of favorite movies than just about any of the others listed here.)