I'm a huge classical music nerd. I'd write simply "Music nerd", but I'm fairly sure the other posters who described themselves as music nerds aren't into the same music I am. I'm a Music History major, if that's any indication (we're like, 6 in the entire music faculty).
I'm also a social sciences/philosophy nerd. I'm pretty much the only one I know who genuinely enjoy classes in all those subjects (except economics, which I find dreadfully boring, though I recognise its importance).
Of course, I'm also a big video game nerd.