The iCade Mobile is a gamepad attachment for iPhone and iPod touch that adds a for-real d-pad, four face buttons, and four shoulder buttons to the sides of the device. Once cradled, you'll be able to position the phone in either portrait or landscape. Both the Core and Mobile are due in 2012; the Core hasn't been priced, but the iPhone gamepad will retail for $80, which seems like rather a lot for some buttons.
Engadget also discovered a prototype at iCade's CES booth for the "iCade Jr.," a teensy, tiny arcade cabinet for iPhones. The release details for this are still undetermined, but how fun! It seems really impractical to play games with a minuscule arcade stick and tiny, tiny buttons, but it's still far more practical than no buttons.
Ion Audio iCade Core
Ion Audio iCade Mobile
Apple iPad Air 2
Apple iPhone 6s