I have trouble with plain water. My go-to drinks, non-Protein edition:
Vitamin Water Zeros. (My personal flavor ranking is: Gutsy, Shine, XXX, Squeezed, Power C, Look, Ice.... Ice is the only one I won't drink). I will mix a Lemonade flavored one with a Peach Iced Tea -flavored Crystal Light/Great Value packet to make an Arnold Palmer. I like that each flavor has a different vitamin/mineral profile, so drinking a variety of them helps me with any vitamin absorption issues.
Nature's Twist Strawberry Lemonade sugar-free drink (find it at Sams)
For Texas people, the H-E-B Multi-Fit waters are very good.
After my daily walk, I drink a Propel water. Has a high sodium content, so it is a good way to replenish after sweating so much.