I've tried so many different whey protein products that it was a breath of fresh air to find one that I could finally settle on. Optimum Nutrition hit a grand slam with their 100% Whey Protein line. They offer a mere sixteen flavors, from generic flavors like Chocolate, Vanilla, and Strawberry, to the more exotic flavors - Banana Creme, Rocky Road, Coffee, Mocha Cappuccino, etc. I hardly ever find myself bored with the taste because ON always has a new flavor out for trials.
On a price per per serving standpoint, you'll be hard-pressed to find a better deal. The standard size (5 lbs.) yields more than 70 servings per container and can be found within the price range of $35-$45, depending on where you order from.
Mixability is never an issue with ON 100% Whey. I've always found that it mixes well with both water and milk using a shaker cup or blender. Using a spoon might leave a few clumps here and there, but nothing too major.
Overall, I'd say the entire ON 100% Whey line is an absolute killer deal. Great price, great taste, great mixability... you can't go wrong!