I am currently reading "Men of Tomorrow" by Gerard Jones.
Not only do you find out how characters such as Superman, Batman, and Wonder Woman came to be (which is fairly common knowledge), but also characters such as Green Lantern, Aquaman, Captain America, etc.
The book also details the cultural influences of comics, and the socio-economic background of the artists, writers, publishers, and distributors.
I'm finding it very interesting reading.
For anyone interested in history, comics, or both, I highly recommend this.