It really depends on what you want and what you already use. Protein sure, but if you're eating 300 grams of protein from food, it's not a necessity.
Supplements are meant to be used to support and enhance gains and that comes from many places -- nutrients, hormone elevation, increases blood supply, focus, endurence, etc, etc etc, If you're serious, you'll use the ones that'll help you.
It's like asking if you can only do one exercise or eat one kind of food.
Honestly, this is one thing everyone should use no matter what. It ain't sexy but it's a must:
http://proteinfactory.com/shop/product.php?productid=427&cat=0&page=1