Coke Zero. I live on it.
OMG cherry coke zero!!
I've been trying to drink less of it, so I've been buying sort-of-sodas. They're basically only carbonated water with citrus flavor, so no caffeine, sugar, or artificial sweeteners. They're rather refreshing and satisfy my want for something fizzy.
I haven't noticed less caffeine in the evening has made any difference for me though.