I love Rammstein, mainly the heavier songs, such as Stein Um Stein, Morgernstern and Mein Teil, fit the bill perfectly for those times when it gets rough, as too does, as some posters have mentioned, Marilyn Manson.
I find Cradle Of Filth's darker songs to add a great ambient mood for romantic sex.
I dunno if anyone here is into them, but a band called Kittie, a foursome, all girls, kind of a death metal band, fucking great to get it off to, especially after a little pot.
I think my all time favourite though, are a swedish band called Draconian, very very dark, satanic lyrics for a large part, but really melodic, with an enormously talented female vocalist, she has a beautiful voice, and sings in an operatic style, the most amazing music to make love to EVER%)