Club Mate is a yerba mate containing soft drink that has become more and more popular in Germany.
It's said to be an aquired taste and in fact noone I know liked their first drink of Club Mate (including myself). However, once you are 'used to it' it becomes a nice refreshing drink (which I, at least, would prefer over coke anytime).
Unfortunalely, its availability can be rather limited depending on where you live...
While trying to recreate it, we came across other people's attempts, and all of these recipes (including this one) are in principle fairly similar. (Not a comprehensive list, but check out these: http://interlockroc.org/2010/04/17/open-mate-beta-2
However, the recipe we came up with is very easy to make and tastes "delightful and surprisingly close to Club Mate", only "maybe a little less sweet".