I'm not sure where else this works, but it works on the US iBooks store. But if you go to your iBooks app and then to the store, there's like 100 books from Kaplan for free.
There's a lot of books for the GMAT, GRE, SATs, law and medical books.
I saw this promo on lifehacker earlier, but since nobody has posted it here, I'm doing my do diligence
If you are on your iPhone, here's a link that opens the iBook store directly to the Kaplan books...
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