Amazon has a new 20% coupon for Optimum Nutrition Gold Standard 100% Casein Protein Powder, Chocolate Peanut Butter, 4 lbs
Combine it with Subscribe & Save option to get another 5% off and free shipping.
The final price is $37.45 (or, if you have 5+ subscriptions this month, $32.45)
Coupon works on other flavors as well.
Note: this is a new coupon. I got the same deal on Black Friday - today it re-appeared again, allowing me to order another jar.