If I may chip in my opinions...
Like Iolanthe said, I'm pretty sure Shuster and Siegel based Superman off of Moses. However, bear in mind that Superman has since had 70 years or so to develop in predominantly Christian country, and Joe and Jerry didn't exactly have exclusive author control. Moses himself was/is a messianic figure, and so it's very easy to make the transition to Christ.
Personally, I've always been annoyed by the movie's attempts to forge a Superman/Christ parallel. The one thing they do have in common, however, is the messianic archetype. This is not a coincidence; Superman was, AFAIK, intended as a messiah from the beginning: A powerful figure, saving helpless people from oppression and crime. The difference is in the messianic type: Secular vs. Religious.
As Lynn stated, Superman saves people physically but not spiritually. What bothers me is when people try to blur that line or cross it. Heck, it's the very reason my Mom was uncomfortable with me watching the cartoons! o_O
