This is really tough. There are tons of great themes from Italian Westerns!!
There are the obvious ones, for me, like: "Titoli" from A FISTFUL OF DOLLARS, the title theme from FOR A FEW DOLLARS MORE, and many many more.
One theme I absolutely adore is Ivan Vandor's title theme for Questi's IF YOU LIVE--SHOOT! (aka, DJANGO KILL!). I find that song haunting and invigorating all at the same time.
I also have to make mention of Francesco De Masi's fabulous main themes for SEVEN DOLLARS ON THE RED, JOHNNY HAMLET, KILL THEM ALL AND COME BACK ALONE, THE MOMENT TO KILL, and many many more.