$6 microphone (ships from the UK)
reviews here (amazon uk)
comparing the gembird microphone to the canon 5d2's microphone
(not mine, but what sealed the purchase for me)
sample real life footage
I know there are plenty of audio improvements for the canon 5d2 that range from having an external microphone such as a rode stereo microphone pro, zoom h4n microphone, rode ntg-2 shotgun mic, to wireless microphone systems including the sennheiser G3 system, sony uwp-1, azden 310 LT... however all of these are quite expensive alternatives to achieving better in-camera audio. Additionally, most of these systems are directional or require the subject to wear the system for higher fidelity audio.
But for those of us who just want to improve the internal audio from the canon 5d2, look no farther! In comes the gembird microphone. This microphone plugs into the external 3.5mm slot improving the audio levels dramatically without sticking out too far from the camera. The best part about this microphone is that the microphone is actually omnidirectional even though the microphone itself appears to be directional by design.
You will want to get a wind screen for this microphone to reduce the wind noise. (i salvaged a headset microphone windscreen which fit quite nicely).
Worse case scenario, if you find that having the microphone on the camera to be intrusive to your left hand, you can always relegate the microphone to it's intended purpose of improving the audio quality on your laptop for skype purposes.
Just wanted to share what I found! In my opinion, this microphone is pretty slick.