The all-new Mikey is the perfect tool for mobile recording. Featuring two custom-tuned Blue capsules for stereo recording, a line-input, USB pass through and a stylish updated 230-degree rotating design. Mikey's three gain settings allow for a versatile recording experience for everything from a loud concert to a whisper. Record lectures, voice notes, live music, interviews, and more. Mikey also comes with its own soft carrying pouch for convenient storage and protection while on the go. Mikey turns your iPod into the coolest mobile recording device around!It's $79.99 at Amazon: Blue Microphones Mikey 2.0 iPod Recording Microphone
Another alternative for those looking for small, portable recording is the $99 Zoom H1 Handy Portable Digital Recorder.
There's something about the idea of using one device - your iPhone - to do everything, that is very appealing. On the other hand, if you buy the Mikey, you have an extra device you still have to remember to bring along. And the other things you have to watch out for: getting a phone call while you're recording! [Seriously; I had that happen the other day while using the iPhone to record something, so I'm thinking I might get the Zoom H1.]