Below is my list of elements that a book or movie must contain in order to be a "western". To me the Lonesome Dove series encompasses more of these elements than any other I can think of. There is more to the West than just wearing the clothes and having a shootout. Look it over and see if you can add anything.

Banjo player
Bank / Robbery
Barber
Bath
Battlefield
Bear
Blacksmith
Bounty Hunter
Branding cattle
Breaking horses
Buckboard-wagon
Buffalo
Bunkhouse
Burial
Cabin building
Cactus
Campfire
Card cheating
Cattle / Horse Baron
Cavalry / Army
Cemetery
Chickens
Chuckwagon
Church
Colt revolver
Courthouse
Covered wagon
Coyote
Desert
Doctor
Dog
Dramatic music
Dynamite
Easterners
Fiddle playing
Fistfight
Fort
Gambling
Gatling Gun
General Store
Grass fire
Gunfight
Hanging
Harmonica playing
Horse thief
Indians
Knives
Land grabbing
Laying rails
Livery stable
Love interest
Majestic landscape
Miners
Outlaws / Bad Guys
Pigs
Plains
Posse
Prison
Rabbit
Railroad
Ranch hands
Ranchers Daughter / Wife
Rattlesnake
Restaurant
Rain / storm
River / Stream
Rustlers
Saloon
Scalping
School
Settlers / sodbusters
Sheep
Sheriff / Marshall / Jail
Shotgun
Smoke Signals
Snow / Blizzard
Stagecoach
Stampede
Sunset
Telegraph
Tough foreman
Town under construction
Trading post
Trappers
Undertaker
Vulture
Wedding
Whores / saloon girls
Winchester rifle
Woman being mistreated
Youngins

just my 2 cents

Rinky-tink player piano (you don't necessarily see it, but you can always hear it when you enter the saloon.)
Texas Ranger
Sourdough prospector with a laden burro
Steamboat

Can't forget the sidekick.

Gotta have a drunk (often times the doctor, stage driver or sidekick).

CC Griff

Gratuitous cleavage!

....maybe I'm thinking about this too hard, but, as all great stories, there needs to be a preavailing good vs. evil and/or man vs. nature.  Also, there needs to be a message or lesson about life.  Other than that, I second the motion on cleavage!

But every movie needs cleavage, not just westerns.

I would change "Women being mistreated" to "Women needing rescue" and add the following:

A magnificent soundtrack
All firearms shooting BP (before 1895)
Firearms shooting no more than the correct number of maximum loads
Characters seen loading and re-loading their firearms esp c&b
Seeing the smart gunman immediately replacing spent rounds
No more stupid fanning
Hunting and living off the land
A fine Irish tenor
My lovely redheaded wife and me as extras on the set  

And most importantly:
The haunting sounds of a Spanish guitar ballade on a quiet evening.  

Beans
Water canteen
Running out of revolver bullets but have plenty on the belt.
Throwing the empty gun away.
Big hair on the ladies.
Very pointy breasts
The meal brought to the guy in jail with a gingham napkin over it.
Derringer in above
Spaghetti westerns where the hats are just so wrong.
Willow pattern cups
Chaps