I have a Rigid cordless impact wrench (14.4 volts if I recall) and it is a great little tool. I have 6 DeWalt cordless drills (hammer and standard), 3 are 18v, 2 14.4 and one is 12v. They have held up great. I also have the 18v DeWalt finish nailer, cut saw, circular saw and light and they have held up great to general construction use. The circular saw is great to take up on roofs to cut in a vent or trim a sheet of plywood that wasn't cut properly on the ground. The cut saw gets used almost daily and is a great tool for any contractor or home owner.
However, I dispise the Craftsman cordless drills. The new ones are terribly gutless and the old ones were better but still very weak compared to the DeWalt competition.
I do second the recommendation to buy the kits. You get a lot of tools for not very much more. DeWalt had the 6 tool 18v kit last year that had the hammer drill, cut saw, circular saw, angle grinder, light and impact wrench. It was around $600 but I almost bought another set just to keep in the barn as they are so handy.