Which one? With the others on the list, I'm assuming the original from 1960 (I do like the remake of The Magnificent 7, though)?. If so, my list goes:
Tombstone
Unforgiven
Magnificent 7
The Good, the Bad and the Ugly
Lonesome Dove
My all-time favorite western is The Searchers (which is also in my top 5 all-time favorite movies)