Well for modern folders, your best option is Kershaw. Traditional folders are Buck. Fixed blades are both Kershaw and Buck, depending on which models you like more.
The real question is why are you limiting yourself to only US made knives? A lot of the good brand foreign made stuff is just as good of quality, and usually cheaper. If nothing else, expanding to foreign too gives you that many more options.
Bah, forgot the UKPK. If you can find a leaf blade one (unless they changed the other one to BD1), you will not be the slightest bit disappointed in it. I was a bit unsure about the lack of lock at fist, I would be lying if I said that I didn't LOVE it. It takes a crazy sharp edge in almost no time with no effort, holds the edge better than any sub-1% carbon content stainless, and the knife comes with an awesome finish on it.