I don't really drink "normal" tea, but I like herbal teas, cold mint tea is really good!Water with lemon/lime slices
Sparkling water, a squeeze of lemon juice and ice
Homemade sugar free ice tea (I just brew the tea normally, add some lemon slices and mint leaves, let it cool and stick it in the fridge. Best drink.)
I don't find alcohol very refreshing as it ends up making me feel warm and sluggish, even if it's a cold drink, but if I must pick something, I'd go for a very very cold sauvignon blanc.