Flashback is available right now in the App store. It's a port of the Amiga version of the game, done by platform newcomers Manomio LLC, and features the requisite touch-based controls and a redesigned menu system.
We'd like to say that this iPhone version of one of the greatest games ever made is a surefire hit, and you should download it immediately, but, frankly, we just don't know. It could be another Mega Man 2, which is an amazing game on just about every platform besides the iPhone.
Flashback ($4.99, Manomio LLC)