Are you interested in the Golden Age of comic books? If so you may want to check out “The Golden Age of Comic Books” website hosted by Bill Jourdain.
The Golden Age ran from the late 1930’s (Action Comics #1 is usually considered the beginning) to the late 1940’s. When the switch out of the Golden Age occurs is a subject of much debate. If you are a fan of the old collectible books take a look at Bill’s site, I think you will enjoy it, I know I do!