I'm looking for some seinen's with a lot of action and that aren't afraid of showing a few decapitations/baby eating etc. Just from the top of my head I'll list some I've enjoyed.
Hellsing Ultimate
Black Lagoon
Attack on Titan
Hitsugi no Chaika
Kill la Kill
Elfen Lied (Honorable Mention, I was still new to animu)
Gurren Lagann
Fullmetal Alchemist Brotherhood
Fate/Zero
Deadman Wonderland
Cowboy Bebop
Freedom
Evangelion
Berserk (Started watching it and liked it a ton, so much that I wanted to read the manga first but got too lazy and quit both)
Knights of Sidonia