Manga:
Battle Royale
B Reaction
Tenjou Tenge
High School of the Dead
Futari Ecchi
Melancholy of Haruhi Suzumiya (frankly, you're better off finding that Wiki that has the actual novels)
Ai Ren (this is insanely deep and is NOT what it first appears to be; it covers some pretty sensitive issues)
School Days (big WTF here)
Rurouni Kenshin

If you like the "clueless guy surrounded by girls" harem sorta thing, there's
Ichigo 100%
I"s
Love Hina
to-LOVE-ru
Lilim Kiss


Anime:
Rurouni Kenshin
Samurai X (the movies of RK)
Vampire Hunter D (original and Bloodlust)
Casshan Robot Hunter (NOT Casshern, a live action version)
8 Man After (not the original, horrible series)
Vampire Princess Miyu
Bastard!!
Doomed Megalopolis
Majutsushi Orphen (really awesome if you like the fantasy thing)
Ninja Scroll (movie and series)
Shadow Skill
Teknoman
Tekkaman Blade
Tekkaman Blade 2
Wicked City
Wrath of the Ninja
Spirited Away
Princess Mononoke


I have a few others on my list, but you didn't really say what you were into, so I picked things based VERY loosely on the Death Note genre (seinen, action, sci-fi, mystery, horror, drama).

Whoops.  You should be able to find everything on
www.onemanga.com
www.mangahut.com
www.mangafox.com

...Need to register an account for fox, though, but, meh.

Wow! Thanks! This list looks awesome!

I probably should have been more specific, but if things are even a little bit based on the Death Note genre, I will probably enjoy it. I really appreciate this!

Sure thing.

And, yeah, Death Note was kinda unique...  I know there's actually another manga out there that puts someone in control of others' lives, but I forget.

Oh, Armitage is also an awesome anime.  Forgot to add that.  XD

lol Thanks a lot!