Ooh, birch beer. There's a pizza place near my old house that still sells it from their fountain. Although, it's not that great; just a sort of light cola dyed red.
The best I've had was real birch beer, and root beer for that matter, in Pa.'s Amish country. Certain farmhouses sell the concentrate. I tasted a drop of it straight up, and it's nasty on its own, so you need to add a ton of sugar to the carbonated water.
I was thinking of trying agave syrup with it next time, or maybe stevia.
Casey, we mostly drink unsweetened iced tea, especially when we eat out. So much so that it's one of those things that we use to judge the restaurant's first impressions, along with the bread and the initial service. If the service is quick, and the bread is good, AND they have good, unsweetened iced tea, it's usually going to be a good meal.
Have you ever tried Korean bori-cha, or oksusu-cha? Unsweetened roasted barley tea, and roasted corn tea, respectively.
If you like unsweetened tea, you'll love these. Served hot or cold, they're frighin' addictive.