Death Note is really an odd man out, there really isn't anything too similar that's any good. But I can go off from the tangent and reco:
We'll start with the obvious and move from there: If you've never seen Akira, watch it. Right now. Same goes for Gantz. You can stop Gantz at episode 13, everything after kinda sucked outside of the "hey cool, tits and gore" aspect. Paranoia Agent, which I think at one point the Americans bastardized with an awful dub, is very good. The writer/director also did Paprika and Perfect Blue, 2 of the best anime movies to have come out. Ghost in the Shell (OBVIOUSLY) and all media spawned from it (a series, an OVA, another movie, etc.) is also extremely good. Cyber City Oedo 808, if you're into that complete bad ass Sci Fi Cyber Punk shit, is 3 episodes of pure awesome. The Dub is excusable for this one, due to the delivery on the lines being so bad that every line is a joke. That and the added 2000000 uses of the word fuck. Darker Than Black, which aired 2006, is a pretty good one, but it feels lacking of closure. Evangelion, another one, if you haven't seen it? Watch it. THey're currently remaking it, and it's turning out as good/better than the original, but the original is still needed to full grasp. Planet ES is a great one, it's not exactly much action, but about a man who works for a space station, collecting trash. Seriously. Amazing shit. Keeping in space, the recently made Moonlight Mile Season 1 and 2 are beyond grand. Granted, that one starts on earth. It's about a man's journey to beat his friend to the moon. They take different routes to do this, and it goes from there.
That should be a good start? I stuck mostly with Scifi/Cyberpunk action/drama with a little mecha tossed in. If there are any other genres you need, ask.
