The Fling tactile game controller is a real joystick that attaches to your iPad so you can instinctively feel what you're doing with your thumb and increase your accuracy.
Xbox and PlayStation controllers taught console gamers to use a left thumb joystick for movement or aiming. Action games on the iPad simulate that with a virtual joystick controlled with your thumb on the touch screen. Problem is, there's no touch feedback from the iPad's flat glass screen. It's hard to keep track of exactly where your thumb is, making games like GWars:Touch or Rage HD harder than they need to be.
Fling is a physical joystick giving you real feedback. Use the suction cups to position it properly centered for the game, then use your thumb on the thumbstick to control the game. The joystick is made by Ten One Design who came up with the Pogo Sketch stylus for iPad, so they're experienced in making touch input devices with great accuracy.
The Fling FAQ confirms you can use two of these for "dual joystick" games, but points out that most first person shooters and role playing games only use the left joystick, while the right side of the screen has virtual buttons instead.
Watch the Fling iPad joystick in action on YouTube and visit Ten One Design on January 6 to pre-order.