I have downloaded and played with several iPhone games (on my iPod touch) and xPlane is the prettiest one so far. X-Plane, X-Plane Airliner and X-Plane Helocopter are iPhone adaptations of X-Plane for the PC. The game is an effective port of a PC game to the hand-held device with multiple views and instruments.
X-Plane has 6 different planes, Airliner has 6, and Helocopter has 4. All have several airfields to fly to, though the terrain is rather generic. Each also has both visual and instrument flight and multiple views of the aircraft in flight. For someone interested in flight simulators, the quality of the graphics, and the overall quality of the game make this is an provocative game.
There of course has to be a dark side. The accelerometer is too sensitive, a slight twitch, like tapping the screen to access one of the other instruments or views will set your plane to whabbling. Finally the cost. X-Plane is $9.99, X-Plane Airliner is $4.99, and X-Plane Helicopter is another $4.99. for the whole package that is $20 for limited functionality, the full PC version is only $39. If the whole package was in the $5 price range, I would highly recommend it but at $20, the limited functionality provided by the iPhone makes the price too much.