1. Multivitamin- I'd say this is far and away to most neglected supplement by most people these days but honestly it shouldn't be. A multi is extremely useful because it is like your diet's insurance policy. Some days we don't eat all the things we need to be as efficient as possible and get our micros but those can go a long way with performance and overall health.
2. Fish oil/flaxseed oil/cod liver oil- We all know that the omega-3 thing is a big deal right now but the sad thing is that most people don't know why. Well.. in short the regular consumption of these oils WILL increase cardiovascular health and brain function which will in turn lead to an improvement in performance and again overall health.
3. Glutamine- Although most amino acid profiles in whey protein powders do have at least a small dosage of glutamine, its rarely ever enough. This amino acid will drastically reduce recovery time and help in the process of building new muscle tissue at about 5-10g a day. Glutamine powder is a godsend and I'd recommend it for any serious lifter.