alot of bands i listen to i heard from tony hawk games. they have awesome soundtracks. i also use pandora. it lets you type a band/song you like and it finds simmilar ones.
I find some from the radio, some from movies i watch, mostly by my friends. Some of then listen to 100% the same things i do, so they suggest me stuff : )
Sometimes i just go "hey this seems nice, i'll download the discography"..