Diet Coke is actually a different drink altogether from Coke Zero, a different formulation. Coke Zero tastes like regular Coke; Diet Coke tastes like metallic ass. I don't see how anyone could drink that much of it or swear by the flavor.
I really want some Cream Soda Dr. Pepper but it hasn't found its way to my store yet.
Also I dunno if you get Caribbean or Latin American soft drinks (you're in Manhattan, right? Go to a bodega) but I'd put Inca Kola and Kola Inglesa (neither is a cola) firmly in with Tiffany.
There's a purple Latin soda that's supposed to be corn-flavored. I've always kind of wanted to try it.