Oh, Lord, Where To Start . . .
Lots of good suggestions.
Ka-Bar, Camillus, Ontario: all good stuff.
Cold Steel, yup, also good.
There is an awful lot of good hardware out there. I own a bunch. Its a serious character flaw.
That said, I do have a favorite type. The Scandinavian designs, embodied in the Mora knives (made by K.J. Eriksson, Frosts, and Normark), the Finnish family of that basic design, chiefly by Marttiini -- excellent stuff -- and the Norwegian brands (more expensive but very well finished), e.g. Helle, Brusletto. I have several of the Eriksson and Frost knives (military, utility, skinners, whittlers). I really like the Swedish Army version and the Mora 2000. Awesome tools.
The Scandinavian grind is a simple single bevel from a usually laminated piece of stock. Shaving sharp and brutally rugged. I have one today that I picked up on a ship in Sweden more than 30 years ago. Its wooden handle is pretty ugly now, but its edge is still very much a working edge.
My prize set is a Finnish (Marttiini) set, a double scabbard with a small 3-inch "puukko" on the outside of a larger "Leuku" knife. The smaller one is a great all around utility knife. The larger one will chop kindling, skin reindeer, and slice tomatoes.
I also have the whole set of Marttiini "MN-x" series of hunting knives (MN-10, -14, -15, -16, and -17). They range from 3 inches to 5 inches (the MN-15 is a very comfortable 4-inch blade) with a rubber handle. Very useful.
Both Ragnar's Forge (
http://www.ragweedforge.com/SwedishKnifeCatalog.html) and Kellam Knives (
http://www.kellamknives.com) cover a wide range of possibilities.
As others have advised, I would not try to get a single knife to do everything. I have a set with a light hatchet and the large & small Marttiini blades. If you can only use two, then a hatchet and a 4-inch or 5-inch utility knife. If you're stuck with just one, then the 5-inch puukko-style utility knife will earn its keep.
The Swedish and Finnish knives are inexpensive (for the most part) and will take all the punishment you can dish out. The high-carbon blades hold a great edge. The stainless blades do quite well, too. I use both.
Oh, and carry a good folder, too. I happen to like the Buck 110 and the Kershaw 3120 or 3140.
You can't have too many knives.