I go for fizzy mineral water. But not the plain or the artificially sweetened, I go for the flavored. I get water in, I get my fizzy fix that I get from soda, and no calories!
You can get fruit infused flavors too. My favorites are Orange, Lime, Mixed berry, and Arrowhead makes a Pomegranate! Usually $1.00 or less for 1.5 liters. =)