It usually will say on the packaging, and if you still are not sure just ask the person that works there and they can point you in the right directions.
They are:
Whey protein
Casein protein
Soy protein
Whey hydrolysates (Peptides)
Protein Blends
This should help http://ezinearticles.com/?Choosing-T...wder&id=250946
EDIT: NINJA'D BY TJOLT. Oh well pretty much said the same thing