While researching the Campbell machine mentioned earlier today, I came across an absurd amount of leather cowboy pistol holsters--not antiques being sold secondhand, but new ones being manufactured today. I wondered what could possibly sustain such an enormous supply, and soon found the answer: The uniquely American pasttime of Cowboy Action Shooting, a/k/a "The Ol' Bang 'n Clang," whereby participants use single-action pistols and rifles to engage of contests of speed and accuracy. (There's a seven-minute vid at the bottom of this entry taking a look at the activity.)
While leather holsters back in the Wild West days were undoubtedly handmade, today's successors are made on machines like the Campbell, and there's a lot more to making them than folding and stitching leather. A good holster will be "wet-formed," then allowed to dry while a plug shaped like the gun it's intended for is placed inside, ensuring a perfect fit. A leather strap, as seen in the holster above by Circle KB, latches around the hammer and prevents it from being accidentally cocked, providing a simple and effective safety feature.The bullet loops in KB's pistol belt are also wet-formed and dry-molded to the precise caliber they're intended to hold, and an appropriate thickness is used so they will not collapse when empty. And all of the cowhide is oiled to provide the desired color and protection against aging and the elements.
Other holster designs use a belt buckle to snug up the fit, like the Rio Bravo made by M. Shelhart & Co., below. It also features an open-bottom design to accommodate longer barrels.
A more simple design is sold by Trailrider Products; their holster below almost looks Italian in provenance, but in fact it's based on an 1863 U.S. Cavalry Pattern.
If you're interested in viewing other examples of fine leatherwork, take a look at Chisholm's Trail, the less-elegantly named Holsters 4 Guns, and a site called Old Trading Post, which features both traditional Western holsters in addition to oddities like an Australian Crocodile variant.
I also came across this rather frightening update on the Western holster: A motorcycle-based variant of unknown origin.
Finally, here's the aforementioned Cowboy Action Shooting video.