This is the scale replica Thor hammer (Mjölnir) bookend available for preorder from Gentle Giant (not to be confused with Green Giant, who's still hocking canned corn). It costs $80 and you only get one, so you better hope your books have something to lean against on the other side. I kind of want one. Unfortunately, Thor's hammer weighs like 300-billion elephants, and my bookshelf is from IKEA and barely survived one move already. You do the math.
Thanks to carey, who has so many books she doesn't need bookends because she has enough to stretch all the way across the shelf. Wow, you must be smart.