The trick, if you are a real cook, is not to buy a set. Certain cookware is great for specific dishes, and you should get the one thing they do best, and then move on to another maker for the one thing they do best.
A cast iron skillet is, in fact, a must. Great for cornbread, fried chicken, blackened dishes, and some other stuff. Lodge is the most popular, but any good cast iron skillet will do. Maybe two -- one large, one small.
A nonstick pan is also essential. Great for omelettes, crepes, and other things you want to cook without too much fat. Bendez makes pans with a great nonstick coating.
A good porcelain-covered iron pot is good for making things on the stovetop that are then baked in the oven. Something like macaroni and cheese, or a casserole. Le Creuset is tops for this type of dish.
A Clay Pot can't be replicated by any other cookware. It cooks and steams at the same time in the oven. Great for Tandoori Chicken, Beef Bourginone, Coq Au Vin, and a lot of other similar dishes. Rommertopf makes good ones.
Then, there's your everyday pots, used for boiling water, making puddings, double boiler stuff, sauces and the like. I have Revereware, but pretty much anything will do for that.
I also think that a pressure cooker is a must. I have a Farberware electric one, and it's great for control, predictability and safety features, but there are also stovetop models that work well if you know what you're doing.
If you make pancakes a lot, then you should consider a griddle. It's easy and cooks them perfectly. There's also no better way to get crisp hash browns than with a griddle. Just get one with a good nonstick coating, or an electric one.
Remember, if you're looking for functionality, a matching set won't cut it. It looks good, but won't perform as well as getting each piece by the maker who makes the best of that kind of piece.