After a bit of searching for something that doesn't taste like a chemical waste dump, I ended up liking the Alani Nu line of energy drinks, but they're normally so expensive that I would never get them. I found a bunch on sale at Costco though, so now I'm set for the next couple of years...
Gamersupps is okay but I haven't found a flavor that stands out to me and they only offer samples of their generic flavors.