Visual Programming Languages – Snapshots by Eric Hosick.
If you are interested in symbolic topic map authoring or symbolic authoring for other purposes, this a a must-see site for you!
Eric has collected (as of today) one-hundred and forty (140) examples of visual programming languages.
I am sure there are some visualization techniques that were not used in these examples but offhand, I can’t say which ones. 😉
Definitely a starting point for any new visual interfaces.