From June 11-17, Starbucks chose "Superman: Action Comic #1" as its free pick of the week. I know it's a little late but you still can find some of the code cards redeemable on Apple's iBookstore. I got one just two days ago.
The comic is really interesting. Superman is a young adult discovering all his special powers and having doubts about the system he's dealing with. The best thing about it? Superman is not that boring good guy we are used to.
So if you wanna take a look go to your local Starbucks and ask about the code card.