Ok, I'll put in El Topo 
The three John Ford Westerns I've seen (Searchers, Iron Horse, Stagecoach) weren't as good as the westerns listed imo. You'll even notice, that John Ford isn't in my 100 favorite directors post, though I like him very much.
And I think the "Neo"-westerns made from the 60's on are the best ones. I'm not really a fan of genres.