YUM!
I use Lean Dessert (made by BSN). I like the vanilla, chocolate fudge, and cinnamon roll. I order either from supplement warehouse.com or vitacost.com - good deals on it - about 1/2 price of GNC.
Also - i have learned the sugar-free coffee syrups (also ordered from supplement warehouse) can really help add flavor to the shakes.
I usually mix the protein shakes with more water than it says on the package - I hate the thickness that makes it feel like you are drinking pudding or cake batter. So package says 4-6 oz water - I usually do 8oz and then mix in syrup and my coffee and have either a hot or cold latte.
also found these two blogs that gives good ideas on shakes too:
http://theworldaccordingtoeggface.blogspot.com/2007/06/my-fa vorite-protein-shake-recipes.html