Well protein powder is essentially a food.
After that I'm not sure there is anything considered a top supplement.
Protein powder is a bit of an in between IMO, I consider it food to some degree, and use it as such when I did use it. Will start using up my current supply in the new year.
But I guess it is also considered a supplement as it supplements your protein intake from whole foods ie steak,chicken, fish, eggs etc etc
Personally after experimenting with supplements I tend to agree with Bazza on this one, I have never really noted any difference when I was using any supplements apart from one……..Protein Powder, obviously gives you essential protein when dieting at a low calorie intake (if using pure powders such as pure WPC/WPI/Egg protein etc). So I find it useful to get your daily protein requirement without adding a heap of calories to your diet.
Having said that I have not used protein powder for several month now and feel no different, but I have put on some weight as I been eating more, so protein would be considered my top supplement.
I also have a generic mens mulit vitamin AM and a night time mulit vitamin and some fish oil capsules, again never noted it making any difference that I could tell, but cheap insurance.
Have also used Glutamine, various Pre workout's, caffeine capsules, creatine in both high and low doses (5 gram being low and up to 30 gram per day being high), BCAA's, ZMA, Test Booster and probably some other stuff found no benefits in any of it apart from the boost from caffeine (but coffee will also give you that).
Again creatine is cheap so are BCAA's so may be try them and see if they work for you.
Have also taken part in the BN test booster trial, did see some results in the blood tests, but did not feel much different, I do remember reporting a bit of extra energy, but looking back might have been a placebo as well, there is a whole thread about it here somewhere.