I practice Bruce Lee's Jeet-Kune-Do, and punching is definetly a huge part of the art. It very much depends on your stance, but for us, our lead leg is in front, about shoulder width apart(diagonally) from the back foot. When you punch, keep your hand open until the last second when you then close your fist, and either snap(for a jab) or go through(cross). In my stance, you have aproximately 70% of your weight on your back foot, and you're standing on the ball of the foot only, so when you hit, you rotate the foot in the same direction(parallel) as your punch, which propels most of your body weight into the punch.
Now that's how I put body weight and legs into it, but then you also rotate your back/chest, and obviously throw your arm into the hit. The upper-body rotation is very important, and also adds a much longer reach, which you definetly don't want to lean-in to get.
If you follow this technique, you use pretty much your entire body for the hit, and you shouldn't be able to punch much harder without strength training.
P.S. huzza @ my first post, good site you got going on
