ishkur has put together a really nifty interactive electronica guide. he has a flash map of genres and subgenres, each with a sound clip and snarky comment. (i like 2-step)
hmm, i’m sure i’ve linked the electronica primer before, but it’s the place to go for history of music genres, as well as a nifty timeline and links. hyperreal’s music resources are also good for more digging. miningco, excuse me, about.com has some really good stuff too both at matthew chinn’s rave/house/techno section and jennifer warner’s dance music section.