1.) The Searchers
John Wayne is so bad ass in this movie the phrase "That'll be the day." became cool. And is some instances still is. It also explores racism which was rarely focused on in the 50's in movies.
2.) High Noon
Was more of a anti-blacklisting film than Western I guess and nothing happens until the end. But the shootout is still awesome, and it's rumored the movie can be viewed in real time. Just watch the clocks. Also Poland seemed to like it:
3.) Stagecoach
Not the crappy remakes that followed but the 1939 version by John Ford. Lot of shootouts and John Wayne kicks ass in this also, which helped him get from the B movies to the A list.
4.) Shane
Same repeated story, tired gunfighter just wants to live in peace. But some conflicts reel him back in and he has to save the lame ass town. But the great part, name a Western in which a guy survives a shootout like that. Also I think Shane survives even though he was wounded. Even though is is seen riding towards the cemetery.
5.) Tombstone
Val Kilmer and Kurt Russel make Wyatt Earp and Doc Holiday the most kick ass gunfighter friends in history. And what makes it even better is it is based on actual accounts from the vendetta ride against the Cowboys. Also anything that features Sam Elliot is a cool movie nonetheless.