TOP 10 Westerns of all time...

The Magnificent Seven,
Shane,
My Darling Clementine,
Texas (1941),
Unforgiven,
Outlaw Josey Wales,
Tombstone,
Open Range,
Stagecoach (1939),
True Grit (the original)

1)The Good, the Bad and the Ugly
2)Once Upon a Time in the West
3)For a Few Dollars More
4)Django Unchained
5)Unforgiven
6)My Name is Nobody
7)True Grit
8)The Treasure of the Sierra Madre
9)3:10 to Yuma
10)A Fistfull of Dollars

The Good, the Bad, and the Ugly
Unforgiven
Rio Bravo
The Searchers
The Man Who Shot Liberty Valance
Lonesome Dove
The Outlaw Josey Wales
For a Few Dollars More
True Grit (original)
A Fistfull of Dollars

Honorable mention for some overlooked comedies:
Support your Local Sheriff (The back and forth between James Garner and Bruce Dern is great)
Maverick

I should also have some Randolph Scott on my list.

There is a difference between my opinion on what are the best westerns and those that are my favourite. The difference is that the favourites are the ones I like watch over and over again. Of my favourites I hope there are some titles that are a worthy surprise.
1. The Good, the Bad and the Ugly
2. My Darling Clemantine
3. The Searchers
4. Stagecoach
5. The Hanging Tree
6. Rio Grande
7. The Big Country
8. Northwest Mounted Police (by virtue of Gay Cooper's character Dusty Rivers)
9. The Plainsman
10. The Gunfighter

Some others not on mainstream lists worthy of mention: 3 Godfathers, Johnny Guitar, Westward the Women.

I don't remeber most of the movies i've seen, but i do rate every one here for the last 12 years... so this is the top 10 western movies according to my rating in IMDB:

1- Nevada Smith (1966) 10/10
2- Lonesome Dove (1989 Mini-Series) 10/10
3- The Outlaw Josey Wales (1976) 10/10
4- Il buono, il brutto, il cattivo (1966) 10/10
5- Once Upon a Time in the West (1968) 10/10
6- Unforgiven (1992) 10/10
7- For a Few Dollars More (1965) 10/10
8- A Fistful of Dollars (1964) 10/10
9- Broken Trail (2006 Mini-Series) 9/10
10- Once Upon a Time in the Revolution (1971)9/10
11- High Noon (1952) 9/10
12- The Missing (2003) 9/10
13- The Treasure of the Sierra Madre (1948) 9/10
14- The Man Who Shot Liberty Valance (1962) 9/10
15- The Proposition (2005) 9/10