You should take protein and creatine as your key supplements or a Weight Gainer product if you want to gain maximum mass. Take a whey protein shake 2 to 3 times per day with one serving being just before your Halo immediately after training and take creatine monohydrate powder or a creatine tablet (like Creakic or Creadex). Start off taking 4 servings per day for the first 5 days and thereafter take 1 to 2 servings per day (2 on training days and 1 on non-training days). To gain mass at the fastest rate, you can either do the Nitro/Cell stack (Nitro 3 times per day and Cell-Tech twice on training days and once on non-training days - always take one serving of Nitro immediately, followed by Cell-Tech right after training) OR you can use a weight gainer like Mutant Mass (along with powdered creatine) or Mass-Tech or Muscle Fuel Anabolic (which already contain creatine). If your diet is good (high in calories and protein), go with the Nitro/Cell stack, if your diet isn't so good, go with one of the mass gainers - start off with 2 to 3 scoops twice daily and increase until you are gaining the desired amount of weight per week (1/2 to 2 kilos).
I've has USN muscle fuel anabolic a couple of times now after switching from the hyperbolic mass. I much prefer this shake because it makes me less bloated and gives me the same amount of protein as opposed to hyperbolic. I find that it's much easier to have a 2/3 of these without feeling too bloated or sick, whereas with hyperbolic mass I found myself not wanting to eat food . I use it mid-morning between breakfast and lunch as a snack, and then lost workout or as a mid afternoon snack if I can't get to the gym, I find that it digests really easily and I can eat all my other meals throughout the day as well so overall it's a fantastic shake and it puts size on well.