Jeremy:

The only suggestions that come to my mind are to check the library &/or web under "Superman", "comic books" or "DC Comics"; check DC Comics' website (http://dccomics.com/); or contact DC Comics directly in New York City. A trip to your local comic book store might be fun and productive, too.

I know that his "S" symbol has evolved considerably since its debut.

Good luck! Sounds like a fun project.

It might be fun to start a thread discussing the impact of comic books (and other vernacular, primitive and bourgois forms of illustration -- and I use those terms respectfully in the artistic sense ) on modern typography. Cartooning, grafitti, folk art and craft and the like could all be on-topic....

David