I haven't tried any of the unusual flavours people have listed, but my favourite fizzy soft drink is Mezo Mix. I've only seen it on sale in Germany, but it seems really popular over there. It's like Fanta and Cola mixed together.

When I'm at home I don't really drink anything fizzy. I'm not a huge fan of drinks with a lot of sugar in them, and aspartame gives me migraines, so I stick to water, coffee, and the occasional fresh orange.