Hi Hooch1,
As Synonym has already said the herb and fruit teas are good as well as the natural infusion range. I use the 'twinings' brand simply becuase they dont affect my sugar levels and you just cool them to make a fruit flavoured drink, extra effort I know but it gets that variety back that I think some of us miss

They are caffiene free too which I think for some of us (not all by any means) can raise our sugars, which if your having problems with other drinks raising your sugars might and I stress might just be the reason if they contain caffiene ... but your already drinking sugar free coke so I suspect this won't be the case.
One thing I will say about the infusion range tho is some of the berry and mixed berry types are very sweet and I couldnt tell the difference from a 'summer fruits' sugar drink but my sugars didn't move at all

give it a whirl and keep your meter to hand and test, others seem to have success with things like green teas (I didn't) but a couple of diabetic friends use them no problem as do others on this board. Other than that I'm out of idea's
All the best.
Richard.