Microphone options
The first three generations of the iPod touch did not have an internal microphone, so you'll need to attach an external mic to use the kazoo and jug instruments. The mic should have a 1/8" connection with four poles.
The current iPod touch does include a mic, so these are not necessary!
from Buy.com
This is the simplest add-on mic for the iPod touch, but does not allow you to connect headphones or speakers while you use it.
from Amazon.com
This is a mic on a cord with an integrated headphone jack, so you can use the mic while connecting your iPod to external speakers.