This is a bit of a follow up to a couple entries ago. Basically, starting at episode 20, Death Note has new opening and ending themes by Japanese metal band Maximum the Hormone. They're already drawing praise and criticism for the style, which is much more hardcore metal than the previous pop-rock themes by Nightmare (Thanks for the correction, Souzou!). Personally, I like the first pair a little better, but there's definitely something exciting about the blood-pulsing energy of the second opening. The visual style of the OP sequence is pretty interesting, too. Ryuk and MisaMisa are totally awesome in it. Take a look:
Edit: Youtube link moved, since the first one went down.
As for the ending theme, "Zetsubou Billy", I'll just give you a 30-second demo download. Death Note 2nd Ending Theme Demo [.mp3, 742kb]