Jules Feiffer's The Great Comic Book Heroes (1965)

Old and reissued in 2003 by Fantagraphics Books. Only got round to read this now and it's one of the most fun piece of comics criticism/personal memoir/pop culture ramblings I've read. Rivals Larry Niven's 'Man of Steel, Woman of Kleenex' (1971).

Check some of it out:

http://www.npr.org/templates/story/story.php?storyId=91746016

My favourite is Chapter 9: "Had I been only 6 years older I could have been in comic books from almost the beginning: carting my sample case in the spring of 1939 instead of 1945..."

In Kill Bill 2, Bill's speech about Superman was taken from here.