Rhythmic light by Fred Collopy
The most full and honorable source of knowledge about light to sound correspondences. Started in 1998 and still growing!
Encyclopedia of Microtonal Music Theory
A very deep resource about all the subtleties and complexities of music theory by [Joe Monzo](http://www.tonalsoft.com/enc/m/monzo-writings.aspx)
A free digital book that teaches a practical introduction to the new foundations of graphic design.
By Rune Madsen
Musical instrument museums online
Explore the world collections of musical instruments
Music animation machine
A life long project of Stephen Malinowski – he manually animates music pieces into nice visual playalongs. He uses blue color for the tonic (C) and accending colors for every next step of a fifth.