After doing some sleuthing in the iOS 5 beta SDK, the folks at 9to5Mac have discovered graphics for the next generation iPad that are 2X the size of the iPad's current, 1024 x 768 resolution. These graphics are capable of fulfilling the requirement for Apple's 'Retina Display' that is currently used on the iPhone 4 and fourth generation iPod touch.
It was originally dismissed when 2X iPad graphics were discovered in the iOS 4 SDK, but 9to5Mac believes that this Retina Display-worthy resolution references the iPad 3's screen.