I listen to rock music. I like bands like Muse and Weezer, who are well known to rock fans, but not so much to everyone else, in this country, at least. I listen to a mix of mainstream, underground and indie. I don't really pay attention to what's popular. I've been listening to Muse for ages, and I used to ask people if they'd heard of them, but they didn't. But since Twilight (ughh...) a lot of people have heard of them, but it doens't change my opinion on the band. Popularity doesn't make much of a difference to what I listen to.
I hate when you find an underground band that nobody had heard of, but then they become really popular and everyone knows who they are. I know it sounds selfish, but I always think "Hey, I found that band first!". :P