A lot will depend upon your body type and your typical diet. But don’t be expecting to become mesomorphic if you’re an ectomorph as I would suspect, given the questions in both this post and another.
Some say the best to use are HGH, Nitric Oxide and Creatine. They all have side effects, mostly mild but you need to be aware of them. If you can get past all the ads on the net there is some good information out there, usually in or around about search page 4 or higher.
But as a reminder none of these or any other product will “grow” more muscle than you already have, they will only assist in making the muscle you have mildly larger and stronger but only with extreme muscle building exercise and a good diet.
Readytoescape is exactly right. The additional bit you need to keep in mind is that some supps like creatine need to be cycled on and off. Continual use leads to ineffectiveness.
For me, the most important thing in addition to clean nutrition with a vit/min supplement are good quality whey protein, additional aminos, lots of water and at least 8 hrs of sleep. Your body doesn't build muscle while awake, it builds while you're asleep. So giving your body the nutrition and sleep it needs is going to give you results.
Also, you'll need to be aware that going off some body building supps is going to make you feel weak, lethargic and you'll start believing you're losing all that you gained. So you need to be careful what you start using if you're not going to be prepared for cycling off of them. I believe the more natural approach is going to do the most good for your body.
I use raw eggs. The downside is the possibility of food poisoning, but I've never experienced that due to the way the eggs are prepared for resale in the US. If you use this approach, eat them just before your workout. After your workout, have a meal with healthy carbs, some protein and healthy fats. But make sure the eggs have been refrigerated, and I recommend you use one yolk per six eggs. So it's mostly egg whites. The yolks are very high in cholesterol, and over time, this can effect your health.