I like good music. I tend to stick with the 90's for mainstream music, but that's because of my age. Seems people's music tastes get locked in between their teens and early 20's.
Examples of "Mainstream" music I like (not counting bands that I liked for years that suddenly got popular):
Fugazi (at least in DC)
Bands that acheived mild success like Ruth Ruth and Rocket From the Crypt
Bands that got famous after I liked them like Mighty Mighty Bosstones, Coheed and Cambria and AFI
Bands that sucked after they got famous like Atreyu and Avenged Sevenfold
I also like metal that will melt your face, weird old punk rock like Television, early-mid 90's emo (not eyeliner and tight jeans garbage, stuff like Pedro the Lion and Jets to Brazil), stoner rock, some surf music
In other words, I keep my mind open and explore music on my own, instead of listening to what Clear Channel got payola to force me to listen to (best thing Eliot Spitzer ever did was busting record label payola)
You won't win this argument, because taste is taste - it differs - some people prefer Mondrian to Rembrandt, others like Nascar collectors plates - it makes the world a better place
Foo Fighters are awesome and one of my all-time favorites. AFI was ok. Mighty Mighty Bosstones had a few good ones.
I like Atreyu and Avenged Sevenfold.
I'm not trying to win any argument. It's cool but it just doesn't make sense why some people just dislike music because it is mainstream and liked by others.