Well, the way I see it, Ramstein is perfect for this. What could be more romantic than a song called "Te Quiero, Puta" (means "I want you, hooker" for those who don't speak spanish).
Or, you may always try out this one:
http://www.youtube.com/watch?v=PTvTLvkiAbI
Now, jokes aside. Back when I was in college I was one of the few guys with a car so I was the usual ride for quite a few girls. And, being a fan of heavy metal and classic rock, you can imagine the kind of reaction I usually got. Also, I am a nerd with a massive Car PC system, so with that system I never lacked space for MP3 files. Back then I invented a cute little tactic wich has served me well for some 5 years now: My hard drive contains about 70% metal, rock, country and 80's pop (the kind of stuff I hear) and 30% girly songs, like Bruno Mars, Colbie Calait, Maroon 5, etc. So it usually goes like this: the girl asks if I'm going her way, I say yes, we both get in the car and the moment I turn on the ignition AC/DC starts blasting through the speakers, followed by the usual reaction of "that's awful" or "we're not listening to that all the way, are we?"; to wich I reply with "press media, then browse files, and pick something you like". The rest of the way is full with "Oh, I love that song" or "I never taught you listened to that, it's so cute!". All that to say, never underestimate the power of music to create rapport.