I keep forgetting to post this, even though it was something I made quite some time ago. Similar to the chocolate, it was less than perfect, though decent if you adore true banana flavor. I don't have any pictures at the moment, it wasn't much to look at.
2 cups of sugar
1 tsp vanilla flavor
1 gallon carbonated water
The recipe is basic. Mash the banana, add some of the sugar and some water and start to simmer. I strained the pulpy mash through a sieve. If I hadn't been so impatient, I would have pureed it beforehand, simmered it and then strained it through a coffee filter. But instead I had little floaties in my syrup. Consequently, there were little floaties in my finished soda, too.
It tasted like freshly mashed banana, of all things. Imagine that. I wanted it to taste like banana cream pie, hence the vanilla. I found myself missing the cream and the pie portion.
Again this is another one that could use more development and feedback.