If you pre-order from GameStop (US or Canadian stores), you'll be given an exclusive SteelBook case with alternate artwork. That's neat, I guess, but doesn't compare to the Amazon pre-order where you'll get the exclusive Griffy familiar, seen in the image above.
This creature wasn't actually in the original Japanese version of the game, so it really is an exclusive here. Griffy can spot enemies that are far away, and has attacks like "Phantom Fangs" and "Petrifying Puff." Griffy can also evolve into stronger forms, called Griffurance, and The Griffrigerator.
Griffrigerator? Really? I'm imagining a refrigerator with a hawk head on top of it with a name like that."
I might have to shell out the extra 10 bucks at gamestop to get that case, hopefully the familiar will be DLC eventually.