Quartz Composer is pretty neat. Also, Yahoo Pipes seems like the web mashups version of QC, but I've never really tried it.

Since the author neglects to mention an example of "a patch-based environment (there are many of these for working with audio)" for audio, I will:

- PD : http://puredata.info/

which is based on (as opposed to "a clone of")

- Max / MSP : http://www.cycling74.com/products/maxmsp

PD can do (simple, afaik - I've never used it for that) video as well but where it really shines is in concocting all sorts of bizarre audio constructs.

Here's my attempt at domain-specific visual programming:

http://opsis.sourceforge.net