Rode Ixy. Capturing high-quality audio with your iPhone or iPad without additional equipment is pretty much impossible. If you need to record crisp video voiceover, classic quotes from your buffoon of a boss, or even organize blackmail that will stand up to courtroom scrutiny, this 24-bit stereo microphone designed specifically for your iPhone & iPad is what you’ll want. $199
Description With Audiobus, the revolutionary new inter-app audio routing system, you can connect your Audiobus-compatible music apps together, just like virtual cables. With a simple and clean interface, easily connect the output of one Audiobus-compatible app into the input of another. Use Audiobus to play a synthesizer live into a looper or multi-track recorder, or use one app to manipulate the live output of another.
iPhone XLR Cable with Headphone Jack for iPhone 3G, 3GS & iPhone 4GS. You can now use your iPhone for professional recording with your existing XLR microphones like Shure, Sennheiser, Audio Technica Etc. This is a good solution instead of using the built-in mic or other noisy consumer microphones. In addition you can monitor what's being recorded, it has a headphone output for monitoring. $29.95