First there were the Tactile+ Plus stickers. Now, there's an exciting new development in the field of fake buttons for touchscreens! The Fling is an analog stick designed to be placed on an iPad's screen, over the virtual joystick. Unlike the Tactile+ Plus, there's no adhesive to apply to your screen -- it uses suction cups.
The transparent design (with a small accent in your choice of three colors) is designed not to obscure too much of the view, and it comes with a lovely pouch for storage when you aren't playing a game with virtual controls or don't want to be seen with some thing stuck to the screen. If you're desperate enough to be playing games with virtual controls on an iPad, then you're probably at the point where you're willing to try crazy stuff like this. You can pre-order it for $24.95.