I'm a big fan of Isopure Protein Drinks. If is a nice change up from thicker protein shakes, comes in a variety of flavors that you won't find in shakes, 40 grams of whey protein isolate per 20 ounce bottle, and is less cloyingly sweet than some other brands. The downside is that it is relatively expensive and hard to find outside of a GNC or Vitamin Shoppe.