In reply to mypyrex:
I use a combination of a GoPro and a Sony CX190e camcorder for filming climbing, skiing, mountain biking, kayaking, kiting, surfing.
If you are just using it trekking then any HD camcorder should do the job. get one that uses SD cards though - its cheaper, lighter and more versatile.
Get a spare battery and get a waterproof case that will allow you to film in the rain and not worry about the camera (like an aquapack or something)
If you are off to nepal or somewhere then you can keep a small battery charged by sticking a freeloader solar charger on the top of your rucksack each day.
No camcorder takes very good stills really. you are better off taking along a decent compact aswell. We just swap the different cameras around between us for a good mix of film and stills of everyone.
It gives you a really great record and you can make really cool films with really amateur equipment.