Elmore Leonard has written a series of superb westerns. Among them:

Hombre
The Law at Randado
Cuba Libre (a sort of Caribbean western, you might say, set in Cuba during the Spanish-American War period)
Forty Lashes Less One
Three-Ten to Yuma
Valdez is Coming

They're all so good that you wish he'd written another 50 books along the same lines. I just don't think it's possible to write a western tale better than he does it.

Here's a website for some info:

http://www.fantasticfiction.co.uk/l/elmore-leonard/