It's OK to admit it—typing on a digital keyboard just doesn't give the same tactile satisfaction as on a real one. The Kiano4 does because it's a real sliding keyboard, rather than flipping, that attaches to your iPhone.
The keyboard rests against the iPhone's rear panel, adding just over a half inch (15.3mm) of width and 2oz of weight. It connects via Bluetooth. The Li-Ion battery holds enough juice for 5 hours of continuous typing and 30 hours on standby. Available in either black or white and compatible with iOS 4.1 and above, the Kiano4 will set you back $100. [iNature]
The Kiano 4 in White
The Kiano 4 in Black