That's what I use... Natures Best Isopure(low carb) Whey Powder. $80CDN for a big pail of it. Before I went with that, I used Prolab Whey... its excellent as well.
Muscle Milk is defintely the best tasting, but it has ~12 grams of carbs per serving, too much for him. Isopure, MaxPro, Designer....this would be alot easier if I were at work right now....