The_Phantom_Empire featuring Gene-Autry, was the first Sci-Fi Western movie. High technology is depicted in an underground civilization. Unfortunately, the special effects and props back then were very limited. This should be updated not only with CGI, but practical effects and sets.
Serenity is a good movie. https://en.wikipedia.org/wiki/Serenity_(2005_film)#Plot
Cowboys_and_Aliens is a very entertaining movie from 2011. https://en.wikipedia.org/wiki/Cowboys_and_Aliens#Plot
Battle_Beyond_the_Stars and Outland are two very different movies, but they are both variations of the Space_Western.
