I'd like to second the nominations of I Ride an Old Paint, Streets of Laredo, and Sonora's Death Row as great cowboy songs. I also loved to hear my grandmother sing Jesse James.

That dirty little coward
that shot Mr. Howard
and laid poor Jesse in his grave

A couple of newer classics are Marty Robbins' Streets of El Paso [=El Paso?] and Roger McGuinn's Chestnut Mare.

LEJ