Link: Ishkur's Guide to Electronic Music.
Not being a huge fan of modern dance music I've stupidly ignored this amazing guide to the myriad permutations of Electronic Music and its evolution over the last 5 decades. While there's tons of info on Techno, Trance, Jungle and Breakbeat there are also wonderfully concise and well written entries on Musique Concrete, Synthpop, Ethreal and Liquid Funk. Massive quantities of sonic samples are available so turn up your speakers (or better yet headphones) and prepare to be schooled...