Nothing all that fancy really
Watch Dogs is a pretty cool game, and if you think you're going to be picking this one up then you may want to take advantage of these pre-order bonuses. GameStop will give you the Palace Pack, which includes an investigation bonus that offers more network missions, and the ATM hack boost that will increase the amount of cash you can steal. Plus you'll get a poster designed by famed comic-book artist Alex Ross.
Pre-order from Amazon and you'll get the Signature Shot Pack. This will include an "exclusive" single-player mission that unlocks a unique Biometric Assault Rifle, and Black Viceroy's outfit upon completion.
Not the most exciting pre-order offers, but they haven't really been that exciting as of late in general.