Fitness professionals get this question on a daily basis. It's not a bad question---it's just not always the best question.
Nutrition, training, and stress management (rest/recovery) are the most important aspects of any health/fitness/performance program. They alone will be responsible for the majority of your progress.
The supplement industry would have you believe otherwise: that if you're not taking the latest formulation, most advanced proprietary blend, you're just wasting your time.
And while there are a few tried-and-true supplements out there, many of them have flimsy -- if any -- research to back up their claims.
This is the most important thing I can tell you about the supplement industry:
The supplement industry is not that same as the pharmaceutical industry. Pharmaceutical companies are highly regulated and must prove to the FDA, over the course of years of clinical trials, that their drugs perform exactly as promised before they can sell them to the public.
The supplement industry, by comparison, is the Wild West. (Almost) anybody can put (almost) anything into a bottle, label it a "proprietary blend," and sell it to you without consequence. There is no supplement equivalent to the FDA making sure stuff works.
But there is this: The Supplement Goals Reference Guide.
The brains at Examine.com have put together an extremely innovative PDF guide that cross-references 20,000 individual studies and organizes them by health goal andsupplement type. Curious about fish oil, or magnesium, or creatine? See what the science says. Want to know what supplements are proven to be effective for arthritis, or increasing testosterone, or helping you sleep? You can search by goal, too.
The only reason I'm reviewing this product so favorably is: these guys don't sell supplements. They have no dog in this fight. They don't care if you never buy another supplement again, or if you shell out big time. All they aim to do is sort through the studies and present the data in an easily accessible way.
And if you're a fitness professional, someone who gets that question all the time---"what supplements should I take?"---you now have a superb reference at your fingertips. I know I'm going to get a ton of use out of it.
Check it out, and if you decide to pick it up, let me know how you like it.