From what I remember, you can carry any folding pocket knife that you want as long as it isn't something weird like an auto knife or a projectile knife. There's no laws against carrying pocket knives concealed in your pocket. And there's no blade length limit in Virginia. The only exceptions to this that I remember are that you can't be a felon and you can't carry folding knives with blades that are over 3 inches long on school grounds. I also think that a couple of cities in Virginia (like Falls Church) have blade length limits of 3 inches.
Just to stay on the safe side of the law, I carry a Cold Steel mini AK-47 (it has a blade length of 2 3/4 inches) because it should be legal to carry almost everywhere in America and because the Tri-Ad lock can't be beat.