Your iPhone is a wonderful point-and-shoot cam and grabs pretty solid HD video. Not so solid? The audio, unless you're recording something an inch away from you in a soundproof chamber. iRig's mic gives you pro-quality sound, mobilised.
It does what you want a microphone to do - you make noises near it, and it records them cleanly and clearly. The build quality is admirable - substantive, comfortably weighty in your hand, a cord that's long enough to give you (or your subject) space, but not enough to turn into a spaghetti mess. In our field test above, our dashing intern Kwame (and the ever-dulcet Joel Johnson) show just how dramatic a difference the iRig makes, versus the iPhone's built-in mic. If you're considering anything beyond amateurish "Here's a 10-second video of my dog doing something funny" video clip, a handheld (or stand-mountable) mic like this would be a must. Singing, speaking, reporting, performance of any kind - all would benefit from the sonic boost.
The iRig Mic's got a variable sensitivity switch, allowing you to toggle how much sound you want to suck up depending on your surroundings or setup. It works fine, but the mechanism itself is hard to adjust. No switch should ever require you to dig your nails into it. As well, the iRig's minijack output, meant for real-time monitoring via headphones, didn't work for me during our tests. A rather large feature to fail, if you're going for pro use.
$US60 at iRig