Does it have to be sweet?
I have recently become addicted to rooibos tea. We buy whole leaf, not teabags, from Amazon and steep it for 5 to 10 minutes with dried organic grapefruit peel (we just save the peel from grapefruits we eat and dry it on the windowsill in the sun), cool it, add ice cubes and enjoy.
I admit - rooibos is an acquired taste, but no harm in trying, right? I guess you could add sugar if you want... I have never put sugar in any kind of tea (hot or iced) so I don't miss it. Good whole leaf tea is so much better than teabags, you just don't want to add anything so you don't distract from the taste!
(Rooibos does not have caffeine.)