"professional" camcorder...

1) Stored file format is "leased compression". Typically, this is DV/HDV - but can be other low loss or loss less formats. There are some pro-grade flash memory, DVD and external hard drive units. NONE apply the compression found in most consumer cams whether highly compressed MPEG2, AVCHD or VOB/VOR.

2) Audio input is generally XLR connectors. NOT a 1/8" (3.5cm) stereo jack.

3) Manual controls are abundant, easy to get to on the outside of the camcorder and at a minimum, include manual audio control, zoom, focus, white balance, shutter speed and aperture... among others. Many consumer cams *might have access to these, though typically not externally (but through a menu system).

4) True pro-grade cam start at about 70mm lens diameter and have relatively large imaging chips.

You did not provide a budget. Start with that.

The BEST hard drive based camcorder will be a miniDV tape based one with an external firewire connected hard drive like those from firewire. The pros will reduce the chances of not being able to capture video. HDD camcorders have known issues with vibration and high altitude. Flash memory and miniDV tape do not.

A short list starting point:

Prosumer:
Sony HDR-FX1000

Pro:
Canon XHA1, Panasonic HDX200, Sony HVR-Z1U, Red Scarlet

There are many others... these are the ones in pretty common use.