Hmm, this is tough one. I don't really have a "favorite" but theres MANY I love. I have to admit I am a sucker for mainstream, but really who isn't? That is why it is mainstream lol.

Linkin Park

Saliva

limp bizkit-(This was my favorite band when I was younger)
I loved the Significant other CD, Chocolate Starfish and the Hot Dog Flavored Water CD, and Results May Vary CD. I wasn't a big fan of Three Dollar Bill Y'all or their newest CD (The Unquestionable Truth or whatever it was called)

Some songs I really love by limp bizkit - Just Like This, No Sex, Nookie, Rearranged, Trust, Boiler, Full Nelson, My Generation, My Way, Take a Look Around, and THE ENTIRE Results May Vary CD.

Hmm, Static-X really gets me pumped for workouts also.

I also love The Game, Eazy-E, some Tupac, and older stuff.