http://diydsp.com teaches you how to make digital music instruments
http://diyinstruments.com has info on building music instruments.
http://exertion.pbworks.com has info on building hybrid generator instruments.
http://diydsp.blogspot.com is my blog on digital instrument design.
http://youtube.com/diydsp has demonstrations of my music instruments.
And check out the subreddit http://www.reddit.com/user/diydsp/m/digi_instruments