Not that the iPhone really needs it, but it and the iTouch/iPod Nano are getting an external mini microphone that plugs directly into the headphone jack. And it's only $US15.
The accessory is also compatible with the 120GB iPod classic (claims its product page), and should be a decent way to conduct interviews or surreptitiously record your coworkers in the adjacent stall. What kind of person takes a dump while on the phone with the credit card company? [USB Fever via Get USB]