I used to mess with a lot of supplements with varying degrees of success. I no longer use any. Here are the ones I've tried over the years:
-fish oil: took high quality fish oil for five years... seemed to cause a lot of bloody noses, and I never ran any faster or felt any better as a result of taking it. i was just convinced that it was a staple for good health. now i suspect it's overhyped
-CoQ10: believe it or not, i actually percieved a slight improvement in aerobic capacity while taking this stuff, although i can't say for that it wasn't just psychological
-ZMA: taken immediately before bed, caused a perceptibly "deeper" sleep state, as many others have reported. i am reasonably certain that this was not just placebo
-tribulus terrestris: supposedly increases testosterone levels by increasing production of leutenizing hormone. i didn't notice shit.
-all kinds of expensive vitamin/antioxidant supplements: never felt any better from taking any of this stuff, but i still somehow derived satisfaction from blowing hundreds of dollars a month on it