sorry, had to go quick there, but anyway - your protein and multi are a given - these 2 are your meat and potatoes of the supplements. then you want a few things - like posted above - amino acids are huge, arginine is for pre-workout because it helps increase blood flow, its your precurser to nitric oxide production, bigger pumps. then beta alanine is for lactic acid buffering - helps you go harder longer. then glutamine is HUGE. its your recovery product, post workout and before bed especially. your body uses this for repairing all the muscles you just blazed in the gym, you'll recover faster, build faster and be less sore. then BCAA are your branched chain amino acids - the three aminos that are essential for building muscle and providing energy. use them before and after. if you get yourself a good BCAA unflavored powder - a pure pharmacuetical grade powder - it will be the worst thing you ever tasted - but throw it into juice or anything sweet and it will be tolerable.
start with that. there is more, but you'll get over whelmed and end up forgetting or hating all the supplements. if you want one more, i'd suggest ZMA. only before bed. it helps you sleep a little deeper and you need the zinc. but dont be supprised if you have these weird crazy dreams at first.
hope this helped.
peace.