"In the old days the hero used to be the quickest on the draw; now, suddenly, the quickest on the draw was the hero." - from Once Upon a Time in Italy: The Westerns of Sergio Leone
The Spaghetti Western Database holds an annual vote to find out what its community considers the essential films of the spaghetti western genre. The more votes, the higher the rank. It then publishes the top 50 as a list of "the most important Spaghetti Westerns as rated by our community."
This is the January 2014 list. The full list of all 139 films that received at least two votes can be found here: forum.spaghetti-western.net/index.php/topic,190.msg162481.html#msg162481