X-Plane is a flight simulator for the iPhone that puts you in of your choice of four different airplanes that you can then take for a spin. This simulator is based off of the Mac, Windows, and Linux version of X-Plane that is actually used to earn FAA certification for actual pilots.
Fans of flight simulators will really enjoy this iPhone app. First off, the controls take full advantage of the accelerometer and the touch screen, so you have to pull back on the iPhone to even take off. After that you can maneuver around using the same control scheme. It's actually a lot of fun. All of the necessary controls are right on the screen as well, so you don't have to switch back and forth or pull up menus. They're also see through, so you can still see your entire flight experience.
The settings options allow you to change all sorts of conditions. You can set the time of day, weather, sky conditions, wind, turbulence, and even select which airplane you want to fly. The area you're flying in has been made to look like Innsbruck, Austria as it has a very challenging environment for you to overcome.
If you like flight simulators, definitely check out X-Plane 9. At $9.99, it may not be for anyone who isn't a huge fan of those apps, but it is very enjoyable. Even for someone with no experience playing a flight simulator before, it is very cool to watch the entire take off and flight presentation that X-Plane offers on an iPhone.