Release date:
July 8, 2008

(click images to see larger versions)

bb1small.jpg

bb2small.jpg

According to Amazon:
Blu-Ray high-def exclusive content: movie cash to see The Dark Knight in theaters (a $7.50 value), 32-page exclusive Dark Knight Prologue book, 16-page comic book adaptation of the first 6 minutes of The Dark Knight, a Batman Begins lenticular, and five collectible post cards.

Not sure about that USB thumbdrive. Perhaps the books are in pdf format and not actual books.