Coincidentally published on the same day as we fell for the ThinkGeek iCade, Apple have applied for a patent describing a portable gaming controller into which a touchscreen device - like an iPhone or iPod touch - could dock into. Apple reckon such a controller could have anything from game-specific controls, like D-pads and joysticks, through microphones and cameras, rumble packs, motion detection or even a second display.
Other possibilities include systems where the docking accessory - which could have an adjustable recess into which the main device would slot - could communicate with other units for multiplayer gaming, or with a nearby TV or media system. That would allow for local audio, visual or other information to be displayed, such as a game map or surround sound effects. The controller could have a battery, too, as well as an authentication chip to make sure you were only using legitimate Apple devices with it.
It's a premise similar to products we've already seen from third-parties like iControlPad, though they generally draw the line at adding controls (and perhaps a secondary battery) to the iPhone rather than anything more complex. Fitting it around an iPad might make for an unwieldy handheld, but seeing as Apple have previously made it very clear that they want a slice of the portable gaming market, the iPhone and iPod touch seem obvious candidates.