Drum & Bass and Dubstep are the mainstream's answer to hard electronic, with gabber and industrial sitting in the subcultural end. The actual heavy end is a genre that doesn't really have an established name, but seems to encapsulate acts described as "noise", "breakcore", "gabba", and "terrorcore". Anything produced by the Bloody Fist label is a sound introduction to this end of things, Nasenbluten being the staple.
Disclaimer: Be careful with acts described as "noise", this term is also used for the more experimental industrial acts, which can land you listening to the same sine wave loop for twenty minutes. Some of the stuff isn't too bad, I don't mind Noisex or Download, but it's not the real thing.