This should be the cornerstone of any muscle building supplements that you decide to take. Multi-vitamins and minerals are very important to almost every critical aspect of a healthy metabolism. This should be especially aparent for the hardcore bodybuilders that are out there. Everyone knows that bodybuilders need more protein and carbohydrates if you want to build muscle. It would stand to reason that if you need extra protein to grow you would probable benefit from extra vitamins and minerals as well. Because of the added stress that bodybuilding puts on the body you will need more vitamins and minerals to maintain good gains in the weight room.
Only 9% of all Americans eat well enough to get the minimal RDA of vitamins / minerals each day. With these deficiencies, it will only translate into less than optimal muscle growth. The important vitamins that you should definately get are vitamin C, B, A, potassium, zinc, and magnesium.
My recommendation as far as multi-vitamins and minerals is concerned is that this is a must. If you elect to take just one supplement at all it should be this. First of all, it is very cheap. I think that I take a Centrum type vitamin that is sold at K-Mart, Walmart, etc. It only costs $7 for 130 of the pills. I usually take 3 a day, one in the morning, noon, and evening after my workouts. Secondly, why leave anything to chance when it comes to muscle gains. If you are willing to spend $35-40 for creatine, why not spend the $7 for something that will obviously do you some good and make up for any deficiencies in your diet.