As a cheap and (fairly) cheerful solution I use a Creative Vado HD mini-camcorder on a suction cup mount. It's a 720p camera with external audio input. On the advice of others here and elsewhere I use a
Maplin telephone pickup coil to record audio. It can be stuck on the inside or outside of a headset (works better inside) and there's no messing about with levels as the auto record level in the camera takes care of it. Also there's no intrusion into the radio/headset connections. One thing I would say is that the audio is very clean and if you want to hear some background noise (engine etc) you won't get much of that. The solution is to have a second camera with a built in mic and do a bit of editing later.
This camera is however subject to a bit of vibration when mounted on the side window of the C172, I might see if I can get some sort of anti-vibration mount for it.
Other cameras that I use are a Canon SX1 which is capable of 1080p video and has a built in stereo mic, and a couple of
these which for £25 delivered from an ebay seller in Hong Kong are very good.
I normally do a little basic editing on the raw video as lengthy flying videos can be
really boring
