A lot of them are from games, mostly Neversoft games (Rise Against, Authority Zero, Bad Religion, Powerman 5000, Alkaline Trio, and a ton more). Also radio... well, internet radio: Yahoo radio (Heaven Shall Burn, I.R.A.T.E.) a long time ago, Pandora (Suicide Silence, Rose Funeral), Chronix Metal, Death.FM, and back when I had the metal channel on digital cable. Then there are the other cases where I go to the local CD store, look at the new release metal wall, and say "that looks cool", then buy it. A family friend gave me about 20 demo CD's of punk/rock/metal a few years back, which had good bands on it. Friends, too (Threat Signal). Some other rare cases, like Deadlock I heard on Heaven Shall Burn's newest CD.