Scorpz:
there are Two different forms of Iron Bone training for the hands.  There is the Karate Method, and the Kung Fu method.  In the Karate method you continually hit a semi-flexible piece of wood with Rope tied around it with the purpose of tearing up the skin on your hands in order to make them harder.  This produces the fastest results, but has to be done over and over again to keep them in condition, produces ugly, mangled hands, and runs the risk of you getting a blood clot and dying from internal organ damage.  Then There is the Chinese Method, which takes about 100 days, however does not damage the hands.  In the Chinese Method, Dit Da Jow Lotion is rubbed on the hands to heal the hands and increase their circulation.  You then set up a canvas bag filled with Mung Beans and Strike it with every surface of your hand Many times, twice a day for one hundred days.  This produces an entire iron hand and not just iron knuckles, and insures that you will still have the use of your hands when you turn 50 

WarriorHawk:
I tried two differnt ways in sync with each other, and it dramatically improved my punch speed. If you have access to an 80-100 lb dumbbell (depending on ur strength), then start doing this. Sit straight up in a chair with a back, or lay down on a bench. Cup your hands around one end of the weight, hold it straight up above your head, and S L O W L Y lower behind your head, only using your triceps. DONT MOVE YOUR SHOULDERS. You will also feel this in your lats, and a bit in your shoulder. Then, once your elbow is completely bent, extend your arms as fast as you can. These are called skull crushers, because if yuo drop it, well... the slow lowering of  the weight builds strength, and pushing it back up as hard as you can builds speed and power.Also, combine this with concentrated meditation. While meditating, concentrate on the feel and weight of your arms. I slowly start punching, while trying to make myself feel as if the arms are getting lighter. Do this nightly, each time longer and harder. After about 3 weeks I already saw improvement.