The Colt Walker/First Model Dragoon. The first really practical revolving pistols, which made all other pistols AND the sword obsolete. These convinced the world's military's that the revolver was practical.
The 1851 Colt Navy. This really generated the wide acceptance of the revolver. With the '51, the revolver became a truly portable personal weapon that could be comfortably worn on the person.
The first true "pistol fighters" used the '51 Navy.
The Colt SAA. There were other cartridge pistols, but none were more wide spread, and like the '51 Navy, gained acceptance for cartridge revolvers.
The Colt Model 1889 Navy. This was the world's first swing-out cylinder revolver, which every revolver since has basically copied.
The Colt Army Special/Official Police and the S&W Military and Police.
These made the swing-out cylinder revolver THE police firearm.
The Colt Detective Special. From 1927 until at least the mid-60's, if you were a detective, undercover, or off duty cop, you carried a "Dick" Special. S&W didn't even try to offer an alternative until the Chief's Special of 1950.
The Colt Python. The heavy lugged barrel has been copied as closely as possible by every revolver maker since. You have to search for a revolver that DOESN'T have a Python-like barrel.
The Colt Trooper Mark III. The worlds first revolver made with molded steel parts, and intended to be "machine" fitted instead of hand fitted, and the first modern revolver to use the transfer bar ignition.
All revolvers designed since use the same production methods and use virtual copies of Colt's transfer bar system.
The S&W Model 27 .357 Magnum. While really nothing but a slightly modified standard S&W revolver, it was the idea of a very high powered cartridge in a handgun that changed the revolver forever.
The Colt .357. The world's first mid-framed Magnum revolver. Before this, all .357's were large frame revolvers. For the first time, a Magnum revolver was small enough, and light enough for every-day carry.
Also introduced the idea of a factory fitted pair of "Target" grips on a service firearm.
The S&W Model 19/66 Again, just a slightly modified standard S&W, but this became THE police handgun for 3 generations of police officers.
For a considerable time, if you were an American cop, you carried a Model 19/66.
The Model 66 convinced the world that stainless steel was the wave of the future.
The S&W Model 29. Yet again, just a modified standard S&W , but introduced the world to the idea of a truly powerful "hand cannon" with enough power to bring down bigger game.
The Ruger Super Blackhawk. There were other large bore magnum hunting revolvers before, but it was the Super Blackhawk that made the "hand cannon" hunting revolver available to the general public.