I've had to record a lot of audio at trade shows like Macworld and CES using the iPhone as a microphone, and while it was okay, it was never ideal. The Mikey by Blue Microphones brings it much closer to ideal. The Mikey connects to your iPhone or iPod using the 30-pin Dock connector (or through a Lightning to 30-pin adapter for newer iOS devices) and turns them into mobile recording powerhouses.
You get two of Blue's custom-tuned recording capsules, which capture stereo sound much better than their small size gives them any right to. You also get 3 gain settings, so you can choose between soft sound sources, like conferences, lectures, board meetings, etc., medium sound sources like interviews, smaller meetings, instruments, etc., and loud sound sources, like concerts, parties, karaoke, etc.
The mic head can rotate through 7 positions covering 230-degrees, so you can set it up just exactly the way you want it. Recording is done through the built-in iOS Voice Recorder app on the iPhone and iPod touch, or an App Store recording app on the iPhone, iPod touch, or iPad. (Yeah, Apple still doesn't give that basic functionality to the iPad.)
You're never going to get the same quality out of a mobile mic that you get out of one of Blue's high end studio mics, but you don't have to settle for tiny, built-in iOS device sound any more either. If you do a lot of recording on the go, and you want to record on the iPhone or iPod, get a Blue Mikey. Your listeners will thank you for it.