Immediately did a Ctrl-F to see if Ishkur's guide had been mentioned on this thread and was not disappointed. As sassy as it is, the deep relational depth and exhaustive Ishkur put into making sense of the whole history of electronic music (and really the /whole/ history -- right back to its origins in musique concrete) made a really big impression on me as a teenager. It's probably a large part of what made me get a double major in music in college.