For more popular stuff you might need to search for the album as well as "download" cause there'll be reviews there as well. I'm yet to look for anything i couldn't find using that.
one day, whenever i see your mum die in front of me, and the police ask me 'can you tell me what you have witnessed' i would say 'i didn't see anything'
torrents and shit for albums or like discography's (the other day i dled like every song the chili pepper's have ever released which is pretty fuckin' awesome).. other than that just limewire for single songs.