Seriously?
iPad: The device is the steering wheel in racing genres. Also, Mirror's Edge is one of the first gaming titles I can think of off the top of my head.
iPhone: Lots of classic titles such as: Street Fighter IV, Assasin's Creed, Sonic, Final Fantasy, et al. Also, a lot of cheat code apps.
iPod Touch: C'mon. It's currently being marketed AS A GAMING DEVICE! Just go to Apple's website, click on iPod, and you'll see: Game On. And on. And on.
Macs (if they count): Steam...