Some Australians have developed a gun controller that is compatible with the Xbox 360, PS3, and PC and doesn't rely on a sensor bar. The device keeps all of the buttons present on the Xbox/PS3 controller, just in a somewhat different layout. The right half of the controller moves to the back as the gun grip, and the left half moves to the front as a foregrip.
The only button, or rather stick, missing is the one typical for looking. Instead, that motion is done by physically moving the gun around. It comes with a bit of a learning curve (trust me, I tried!), but I believe it could make shooters easier in the long run. It definitely makes them more fun to watch.
A few of the buttons' placements seems a bit odd, but I'm sure with a little getting used to, that feeling would go away. Pricing in the US is said to $149 when it launches.