Starting from the left in the above picture we have a Lange style socket. Lange, and the following Tournier socket, are both quite rare and therefore difficult to replace. More common are the "Fat-Boy", or Standard socket. These sockets come in a variety of styles(turn-key, pull-chain, push-button, etc.), and are still easy to find replacements for. Electrolier sockets are what you see on many newer light fixtures. Early on, in the 1950s and 60s, Electrolier sockets were often made of brass, or nickel. Since then, almost all have been made of aluminun and are of pretty low quality, although there are still some solid brass reproductions being offer for a higher price.
The last three sockets use a different sized light bulb. Intermediate was used for appliances and specialy lighting. Finding good quality replacements for these has become nearly impossible, and most times lights need to be retro-fitted with candelabra size. Candelabra sockets are most common in chandeliers and wall sconces. In the early 1900s, brass candelabra sockets were sometimes used in high-end table lamps and, like many antique sockets, brass candelabra sockets are extremely difficult to locate, especially the pull chain styles.
Finally, the Mogul socket. A giant among sockets often found in floor lamps and industrial fixtures. The most common place for a mogul sockets seen today is a three-armed floor lamp with a center socket upon which sat a glass refector bowl. Most mogul sockets are ceramic. The brass one pictured above is extraordinarily rare, as are the Bakelite ones.