The frugal folks at Thrifty Nerd have informed Joystiq that Amazon has upgraded some of its pre-order deals; specifically, pre-ordering Bulletstorm, Top Spin 4 or Killzone 3 will now snag you a $20 credit instead of $10. The credit will be applied to all Bulletstorm pre-orders regardless of when they were placed, so don't worry if you pre-ordered before the deal went into effect.

Thrifty Nerd notes further that both Gears of War 3 and FEAR 3 pre-orders are good for a $20 credit, and there are a number of $10 credits available as well. Check out Thrifty Nerd's pre-order credits page for all the deals.