fresh brewed sweet iced tea. Can't live without the stuff. From my travels I gather that its a southern drink (southeastern US).
Edit: Just remembered this is a favorite soft drink thread.
I have to say Mountain Dew or Welchs Grape.
FYI: in the south all sodas are reffered to as Coke. Im not joking. Example:
Mom: You want a coke?
Me: Yeah. whatcha got?
Mom: Dr Pepper and Mountain Dew
Me: MD