ad Chris: (...) Others:
Eisbrecher
Totenmond
Dornenreich (Another amazing band, although Austrian, not German)
Einstürzende Neubauten
Janus .....
Wow, that's crazy, I don't know any of these groups. Never even heard of them lol. I guess I'll check out the Austrian group first ;-)
I know most of the groups the other posters mentioned. Generally speaking I have to say I do not recommend listening to German rap music (like Bushido etc.). Of course, that is mostly a personal preference but I don't see any possible benefits in listening to their "lyrics" unless you want to impress whoever you talk to with an endless list of swear words and enjoy listening to people talk about how cool it is to be violent.
Some of Bushido's lyrics are just outrageous in my opinion. Young language exchange partners keep asking me how to translate these songs which I respectfully refuse. To each his own I guess. If you like it, go ahead and listen to it but I doubt you will make any progress linguistically speaking (well, of course, you will gain some expertise in swearing and threatening people verbally and after all that is part of a language too; still I can do without it).
My personal preferences aside, I'd say listening to music is always a nice way to immerse yourself in a language.