Comic book letterer Todd Klein has written a fantastic five-part look at the Batman logo over the years, from Detective Comics 27 in 1939 all the way to the recent masthead that debuted with the Hush storyline in Batman 608. See: part 1, part 2, part 3. part 4, part 5.
And a similar series on Superman and Action Comics: one, two, three, four, five, six. Related: Frank Quitely and Grant Morrison’s failed attempts to change the “S” chest logo.