The Searchers would be my number one suggestion but i see it has already been mentioned,some others i would recommend are...
The Magnificent Seven.
True Grit.
Fort Apache.
Rio Bravo.
A Fistful of Dynamite.

There have been so many great recommendations already made in this thread, and almost all of them would have been my recommendations too.
I would like to add one more to this list, which has been a film of some influence for me. Its called El Dorado, starring John Wayne, Robert Mitchum and James Caan. It has had a considerable influence on me because it made me hunt down and watch the Clint Eastwood and John Wayne western films.
The acting of James Caan is notable in this film, where he plays a gambler who cant shoot. It was such a powerful performance by James Caan that I am surprised he didnt get an Oscar for it. Thats my input to this list.:)

just ordered unforgiven. i always seem to watch it when its on. must've watched on tv a dozen times and i thought i may as well own it then i can watch it whenever. also, tombstone, the outlaw josey wales, high plains drifter, the alamo, shane and butch cassidy and the sundance kid.

First, let me say I think it's great that younger fans are rediscovering the western. Westerns (along with Horror) has long been my favorite genre.
Most of the films I'm reccomending have probably allready been mentioned but just in case they haven't, here's a few favorites:

Since you all ready have seen my personal favorite,"The Good, The Bad and The Ugly" you have to complete the trilogy
"A Fistful Of Dollars"
"A Few Dollars More"
You also may want to check out Sergio Leones other classic western
"Once Upon A Time In The West"

Staying with star Clint Eastwood check out these films

"High Plains Drifter"
"Pale Rider" (two westerns with a hint of the supernatural)
"Hang 'Em High"
"Two Mules For Sister Sara"
" The Outlaw Josey Wales"
"Unforgiven" (academy award winner)

With Star Lee Van Cleef:

"Sabata"
"Return Of Sabata"
"The Big Gundown"
"Death Rides A Horse"

With star James Stewart:

" Winchester '73"
"Man From Laramie"
"Night Passage"
The Naked Spur"

and in no particular order:

"Tombstone" (Kurt Russell)
"The Quick And The Dead" (Sharon Stone)
"Open Range" ( Kevin Costner, Robert Duvall)
"Quigley Down Under" (Tom Selleck)
"Silverado" (Kevin Kline, Scott Glen)
"Lonesome Dove" (Robert Duvall, Tommy Lee Jones)
"The Missing" (Tommy Lee Jones)
"The Magnicent Seven " (Yul Brynner, Steve McQueen)
"The Long Riders" ( Stacy Keach)

and last, but certainly not least.. The great John Wayne:

"The Searchers"
"Rio Bravo"
"Stagecoach"
"Red River"
"El Dorado"
"True Grit"
"The War Wagon"
"The Man Who Shot Liberty Valance"
"Fort Apache"
"The Shootist"
and many many others.

These are just the tip of a very large iceberg. The western has been around since the begining of movies and there are hundreds to choose from.
And of course there are dozens of western TV shows, comic books and novels out there too. I hope this list helps. Have fun and enjoy.

It's not your typical showdown at noon western but give The Treasure of the Sierra Madre.

I used to be a huge fan of western movies.
and yeah..the good the bad the ugly ..freakin A' :D

(classics)
Paint your wagon...
River of No Return..
Hang em High
Trinity
Trinity still my name
Butch Cassidy and the Sundance kid
Magnificent Seven



(this is all i can remember off the top of my head)

Will post more when i remember them

if you want John Wayne, just watch Rio Bravo, True Grit, and The Searchers. Then you'll have seen every John Wayne western

and Red River

and El Dorado.

Thanks for reminding that great movie to me in this thread, Kane.

Since all of my favorite westerns have already been mentioned, I'd like to mention them again just to reiterate how great they are:

Once Upon a Time in the West (really the only time Henry Fonda plays a villain--he's excellent; great music; favorite western)
The Good, the Bad, and the Ugly (great ending and music)
Young Guns (the 80's western)
The Quick and the Dead (Sam Raimi's take on the western, great cast, very stylized)
Paint Your Wagon (the musical western w/Clint Eastwood)
Johnny Guitar (Mercedes McCambridge at her villainess best w/Joan Crawford)
Two Mules for Sister Sara (Shirley McLaine as a prositute masquerading as a nun w/Clint Eastwood)
Tombstone (great cast)
Quigley Down Under (a western in Australia w/Tom Selleck and Alan Rickman)
Blazing Saddles (best comedy western of all time)