Not a protein powder, but a suggestion for a 'mixer':
I usually mix mine in non-dairy milk, but I have also used the following , when I want something with fewer calories but with a bit of flavor (rather than water):
coconut water
cashew juice (Amazon offered a free case of this with the purchase of a case of ONE coconut water---the deal might still be on), so I tried it. It's high carb on its own (because of added organic sugar), but mixed with a high-protein powder, you can get a nice 2-to-1 carb-to-protein ratio 'recovery drink').
Herbal tea (can add nutrients and flavor without calories or carbs or fat). I tried a Celestial Seasonings Almond dessert tea, and it was yummy with vanilla protein powder. I'd brewed the tea before working out, in a Thermos, and when I was done, the tea was still warm, and I mixed it with the PP. I don't drink coffee, but it tastes like how I imagine some fancy mocha java thingy tastes!
I suppose you could also use green or white tea (higher antioxidant levels, and at least with green tea, EGCG--which I will not even attempt to write the full name of --epigallocate..fragilisiticexpialidicious!----which can increase fat burning). I can't vouch for the flavor, though!