Hi chongolio !
I think I can tell you that ^^.
Their is two input other than the internal mic on the iPhone. The first is in the jack, which is a 4 points jack, so one more than usual used for the mic input. My favorite mic for this input is the Philips SHH1610. It's really cheap and sounds really better than the more famous iSoniTalk from Monster.
The other choice is hidden in the dock. There is a line-in there. On this one you can plug some more advanced, and better sounding, devices. I personally own the Alesis ProTrack (2 mics + XLR/Jack stereo line-in) and it works reall well, despite the fact that it's not full-duplex. This means you'll need to use the iPhone sound output (instead of the ProTrack one) to hear your recordings.
Have fun

!