Dropship was one of our favorite iPhone shooters when it came out in December, and introduced us to one of the best dual control stick control systems for the iPhone.
The game succeeds on many levels, but perhaps the most critical piece that they got right were the controls. Your ship is controlled by your left and right thumb which can be placed anywhere on their respective sides of the screen. Left thumb controls thrust and right thumb controls the direction of firing. There is a slight learning curve to this control method, but it ultimately allows very good control of your ship and avoids the major problems that come with a fixed button system (using up screen real estate, and accidentally hitting the wrong button).
We're not sure how long this free pricing will last, but there's no reason not to get it now.
App Store Link: Dropship, Free