A cowboy anime? :/

Cowboy Bebop.

okay, it really doesn't have much to do with cowboys, but it's an excellent anime!

Trigun, is some parts is set in the old west.

Gun X Sword is আরো of a steam punk wild west story kinda like Trigun.

I've found that Japanese জীবন্ত like playing around with the wild west theme, but tend to put it in alternate universes and not in America, and thus have very little historical authenticity other than aesthetics.

You'll see an American প্রদর্শনী up in a যেভাবে খুশী জীবন্ত প্রদর্শনী dressed up as a cowboy every now and then too. Like Liz and Patty from Soul Eater, even though they're from New York... Oh, and "Death the Kid" is probably a play on words with "Billy the Kid".