I am always surprised by the number of people who pick the Searchers as JW's all-time best western... I think it is the slowest JW movie ever made and does not have any better cinematography or acting than several other JW movies.
Want to see JW play a "darker" role as in Searchers, but with a far better story line and better co-stars? Try The Man Who Shot Liberty Valance. That's tied as my all-time favorite JW movie, along with Rio Bravo. (Fantastic supporting cast in Rio Bravo, which is what makes it slightly better than the two similar JW movies.) I like all of the post WWII JW westerns, except The Searchers...
As far as other westerns, The Magnificent Seven is an absolute classic. The Professionals and The Wild Bunch are outstandingly entertaining and pretty darn good portrayals for the turn-of-the-century time period. The Outlaw Josie Wales is the one pre-Unforgiven Clint Eastwood western that lives up to decent story line, acting, and production standards. There are a couple Charles Bronson westerns that aren't bad too. I like Pat Garret and Billy the Kid if for no other reason than the double-barrel shotgun loaded with dimes!
For modern westerns, I really appreciate the quality in Dances w/ Wolves, Tombstone, any of the Tom Selleck/TBS movies (Monte Walsh, etc.), Open Range, and Unforgiven. They all also have great casts, acting, and story lines. I watch 'em all over-and-over again. Conagher is also extremely well shot and acted. Sam Elliot just exudes "Cowboy."
I'd love to see an all-star cast western, with Tom Selleck, Robert Duvall, and Sam Elliot working together.
There was a western movie shot a couple years ago around here by one of my former bosses. I know just about everyone who acted in it and worked the set. He's had it to several film companies and even took it to Cannes, but it hasn't been picked up. I'm hoping he tries to get a direct-to-DVD-release deal, if no one will show it in the theaters...