As most experts agree, good audio is a large part of a good video experience. Up to now, all small HD-capable cameras (say, the Panasonic ZT7 or FT1) and even including the great Lumix GH1 use autogain for the audio, which you cannot switch off. None but the GH1 (which is hardly portable) have mic inputs. One could record on a separate device, but that is hardly real portability.
There is one and only one exception now: the Kodak Zi8. Amazingly, this cellphone-size HD video camera not only has a stereo mic-in (1/8") with plug-in power - it has audio level control, with meters! You cannot change the level or see the meters while shooting and the compression is 128k, 48khz, AAC but the audio is very good. This tiny camera shoots at 1080p 30fps or 720p at 60fps.