I know A few. Calalini is. It's about a girl named Jani Schofield, who has illusions such as "24 Hours". Kagome kagome is inspired off the game played by Japanese children. (Kagome Kagome is "Circle you" in English.) Dark Woods Circus is, and, from what I know, Hide and Seek has something behind it, too. This is just what I have heard. I'm pretty sure these are the only ones, but, there might be more for all I know.
I know that the song Secrets of Wysteria is based on a true story aside from what was already mentioned.