They include Gamestop and Amazon offering exclusive missions, as well as some boosts in-game. There are also weapons and an outfit. Watch Dogs is out mid-November.
For those ordering through Gamestop there will be "exclusive investigation opportunities inside the network", courtesy of an 'Investigation Bonus', and an ATM Hack Boost.
A free poster by comic book guy Alex Ross is also thrown in for good measure. Those who pre-order through Amazon get to unlock the Biometric Assault Rifle, and a Black Viceroys outfit when you complete their mission.
Watch Dogs releases on Xbox 360, PS3, Wii U and PC November 19th in the US, 22nd in EU. PlayStation versions have been said to feature an exclusive hour's worth of more content. It will hit PS4 at launch.