I'm a music nerd. I know most everyone likes music, and a lot of people love it, but it's pretty much an addiction with me. Sometimes I think I have a problem. I talk about it too much, spend too much money on it, I freak out if I can't listen to it in a car. Seriously, I get legitimately sad (like really sad) if I can't listen to music in some situations. I describe a lot of my life in terms of music. I study it, I make it, I listen to it. And I'm not even in a band.
Other than that...
I'm a TV nerd. I don't watch many movies anymore. The last one I saw in theaters was in December (True Grit) and I don't really have much of a desire to watch any lately in theaters on elsewhere. I marathon the hell out of some TV shows though (right now, its Breaking Bad). I own a freaking box set of The Wire (and yes, I do watch the show repeatedly). Only TV nerds do that. No anime, though. Never got into it (except some Digimon as a kid. I had a nostalgia trip and watched some of it again recently).
I think there have been so many shows over the last decade that have risen the bar insanely high for television (Mad Men, The Wire, The Sopranos, Curb Your Enthusiasm, Louie, Arrested Development, Chuck, Parks and Recreation, Treme, Community, early seasons of The US Office, Dexter, Terriers, Battlestar Galactica, The Sarah Connor Chronicles, Lost, Breaking Bad, and so on until eternity) that films have lost their luster to me.
After that, I'm a gaming nerd. I love games, but I will have periods (months even) where I don't play any.