Creatine
My roommate, and best friend, is able to college because of his wrestling scholarship. Just before the end of the year his coach took him aside and told him to try and bulk up over the summer. He is just doing ok in his current weight class. He could do really well in the next weight class.
He decided to try creatine supplements and it is working. I am impressed on how quickly his muscle mass is increasing. It is not like the Hulk, sudden bulging muscles everywhere. Using the creatine supplements is just adding to what he already had. He is working hard to increase his weight in a healthy way. It is a balance of eating right, taking the supplements and working out. He is very motivated; he is worried about keeping his scholarship. If he keeps using the creatine supplements all summer he will be in a different weight class by fall. It will be interesting to see how well he does in the fall. He is training almost non-stop. He's dream is to be good enough to try out for the Olympic team.