Here is my categorization of Superman history, that I posted on another foum. My bias is pretty clear, I think...

"DC basically makes some big changes to Superman every 15 years or so. Here are the different periods of Superman comics so far, to help you if you buy a lot of back issues, etc:
1938-1956- The Golden Age
The first Superman stories by Siegel and Shuster were published during this time, as well as the Superman Radio Show, newspaper comics, Max Fleischer cartoons, and Adventures of Superman TV show. The Golden Age ended between 1956 and 60, when the Flash (Barry Allen) met the original Flash, and it was revealed that all of the original superheroes from the 30s and 40s were still alive, living on "Earth-2," including the original Flash, Green Lantern, and Superman.
1956-1970- The Silver Age
The Justice League from Earth 1 and the Justice Society from Earth 2 teamed up often, and there were 2 different Supermen. The first was the original from 1938, who worked at the Daily Star and eventually married Lois Lane. The second (main Superman) was Superboy during his teenage and college years, and grew into earth's greatest hero. The Legion of Superheroes was a super-team from the future that started as a Superboy fan club. Mort Weisenger was the Superman editor during most of this time, and brought in characters like Mxyzptlk and the Bizarro World. Silver Age Superman stories that you might buy include the 3 volumes of "Crisis on Multiple Earths," "Superman in the 60s," "Tales of the Bizarro World," and the "Man of Tomorrow Archives."
1970- 1986- The Bronze Age
Began with Superman #233. A lab experiment turned all the kryptonite on earth into harmless lead. Clark Kent took a job at a TV station, WGBS, and characters like Morgan Edge and Steve LOMBARD (not Jobs) were introduced into the Superman continuity. Frequent teamups between Superboy (young clark kent) and the Legion of Superheroes. Ended with Crisis on Infinite Earths.
1985/6- around 1996- the Iron Age
Everything related to Supeman died, plus an extra helping of death. In Crisis on Infinite Earths, released for DC's 50th anniversary, Supergirl and Lori Lemaris were killed, while the original Superman, Superboy, and Lois were eliminated. John Byrne's famous miniseries Man of Steel relaunched Superman for a new generation. Superboy was not included in the origin (a fact that Byrne later regretted) and Superman was once again the only survivor of Krypton...no Krypto, no Supergirl, no Kandor. Legion of Superheroes was left without an origin and detached from "the Superman family" since Superboy had never existed. Superman was killed by Doomsday in 1992. He was resurrected the next year, but not before Coast City, home of Hal Jordan the Green Lantern was destroyed by one of his enemies and everyone in it killed. (Hal Jordan then went crazy and killed the Guardians of the Universe, and then became the villian Parallax. He died saving earth when he took a break from his newfound villiany.) Cat Grant's son Adam was killed. Jonathan Kent sort-of died from a heart attack once, but after he lived one of Clark's childhood friends from Smallvile tried to kill all of his relatives; thus, Clark Kent "died." Finally the entire City of Metropolis was blown up in Action Comics #700.
1996-Present- Silver Age Redux
Kingdom Come was published, a critique of the Iron Age which began a trend toward bringing Silver Age elements back. Technology made by Brainiac was used to restore Metropolis, forming it into the "City of Tomorrow." The Silver Age JLA lineup was brought back, Krypto returned after an unpublished story by Elliot Maggin made him popular again. Kara, the original Supergirl, returned (twice, but that's complicated.) Bizarro is back, the JSA is back, Hal Jordan the Green Lantern is back. Lex became President of the United States and Pete Ross married Lana (marriage is now on the rocks) and was chosen as vice-President. Superman/Batman teamups returned, in the form of the Superman/Batman monthly comic book. Superman:Birthright is the official Superman origin of this period."