Apropos of a recent discussion on the forums, I've started a music theory project on the wiki. The project page can be found here:
http://imslp.org/wiki/Music_Theory
I started to write the first chapter (materials of music), which can be found here:
http://imslp.org/wiki/The_Materials_of_Music
Just letting everyone know that there is - in fact - a theory book now, which I hope people will work on.
