A beautiful naked woman. Or in my case a trick that wears the same size shoe as I do, because I get such a hard on just thinking about waiting until he falls asleep and stealing his shoes.
My next answer would have to be : another round of puberty.
Seriously though, my view on test boosters is a bit negative. I am skeptical that anything can boost you significantly and for a long time. If that were case, you would see these mega million pharmacy companies taking over it and advertising in Golf magazines. I think some things can temporarily boost your test levels for a short time, but after a while the effects are lost on the body and it doesn't respond like it did before.