My personal favorite is ABB (American Body Building)'s Monster Shake.
I pick up a case of 12 chocoloate and a case of 12 vanilla each month at GNC and they cost me about $2.00 a can (using Gold Card membership). Before the gym, I throw one in a small vinyl "bag" cooler, grap a couple of ICEEs out of the freezer to keep it cold, and throw it in my locker. After each workout, a cold shake is waiting!
These shakes have 50 grams of protein, a load of other good stuff, and only 240 calories.
It's all opinion, but I can't find a much better product at that price.