Started my pre-op liquid diet today...
Syntrax Nectar is awesome. It's my favorite. The premade shakes taste like barium. Gah. So chalky.
I advise checking out the Bariatric Foodie site. She also wrote a book devoted entirely to making your protein shakes not suck! I add some decaf instant coffee and unsweetened cocoa to my chocolate shakes, and it is delicious!