I want to mention that I did some investigating about the Automatic
Gain Control (AGC) on modern video cameras about a year ago.  I found
that the Canon HV20 had both a jack for an external microphone as well
as the ability to turn off the AGC.  You then adjust the recording
level with a meter that appears in the viewfinder.  The camera works
just fine, and I have no reservations about recommending it.

I do remember that there were not very many "home use" cameras with
this feature, as it is usually found on the more expensive professional
models only.

Randolph Herr