http://www.macnn.com/articles/09/03/18/thumbtacks.now.shipping/
ThumbTacks mini-microphone ships for iPod touch, Nano
updated 11:25 pm EDT, Wed March 18, 2009
ThumbTacks now shipping
Switcheasy has launched ThumbTacks, an ultra-small microphone for the iPod nano 4G and iPod touch 2G. The microphone attaches to the iPods's 3.5mm headphone jack and allows the media player to be used as a voice recorder. The ThumbTacks microphone is shaped like a thumbtack and measures 1.21 inches by .46 inches, using gold plating on the plug.
The ThumbTacks works with third-party apps on the iPod touch. The microphone is available in red, black and white and costs $13.
Fresh-Faced Recruit
Joined: May 2005
Shortcoming
The problem with these headphone socket microphones is your iPod thinks you have headphones plugged in and disables output to its built-in speaker. Meaning you're constantly unplugging the microphone to hear what you've recorded.