I'm just getting into this genre after all of these years. So far I've seen (not counting the Leone films):
Sabata
Adios Sabata
Django
W Django (aka Viva Django)
Have A Nice Funeral..Sartana Will Pay
And God Said To Cain


On the pile to watch or on the way:
Return Of Sabata
The Great Silence
Cemetery Of Crosses
Death Of A Gunfighter
The Five Man Army
Duck You Sucker
- saw this first run back in 1972 but haven't seen it since.

Also have a few Trinity/Sartana movies/sequels in name only to watch on a very poor looking 20 movies on 2 dvds set called Wild Westerns. Although some are in widescreen they artifact like crazy and some faces are blurry squares. Pretty much headache inducing.

"The world's going to change tonight, doctor, I'm glad you'll be able to watch it. And... happy Halloween."