Books sort-of-about cowboys to whatever degree that I have read and thought excellent but as yet not seen a movie or television adaptation of:
Lonesome Dove
Blood Meridian
All The Pretty Horses
Butcher's Crossing
Books etc and so on where I have also watched the thing:
True Grit, both movies are worth a look for different reasons. It's pretty standard cowpokin' though I guess, not exactly anything else to say.
Sisters Brothers as mentioned, it's pretty funny.
The Revenant: surviving bleak conditions for a long time.
Ones where it's just the movie or TV I have experienced in most cases even if there is a book:
Hateful 8: Quentin Does Cowboys and it's exactly what you'd anticipate.
Outer Range: Nice setup, waste of time execution, avoid this.
The Ballad of Buster Scruggs: Coen Brothers Do Cowboys (again) and it's exactly what you'd anticipate. Provided a handy "First time?" meme to the Internet.
3:10 to Yuma: Cowboys and Trains, just like they used to do, so standard action really.
The Assassination of Jesse James by the Coward Robert Ford: Can't really remember, but it is well-regarded so perhaps I will try again. I think Nick Cave has a cameo in it for some reason.
The Proposition: They have cowboys in Australia?! Nick Cave wrote this and did the soundtrack with Warren Ellis.
Tombstone: I have noticed people recently saying this was an overlooked gem and have intended to get around to watching it and finding out if they're right.
Then assorted Sergio Leone and Clint Eastwood and Kevin Costner of course.
EDITED: 17 Sep 13:52 by MILKO