In case you haven't seen it before:
http://techno.org/electronic-music-guide/
BAM. I've been browsing this for literally hours. It's really mind blowing to see how the genres cross and evolve over time. I also did a game where I gain a point every time I knew a track. My current score is like 5.
And if you guys want to go even FURTHER,
http://furia.com/misc/engenremap.html
This one is much, much, less accurate, as it is procedurally generated, but just look at the genre count!
I don't really expect this to turn into a discussion, but I wanted to show you all this. :D