If you liked
Shinseiki Evangelion
|
...then you might like
Mahou Shoujo Madoka★Magica
|
Both are much darker deconstructions of typical anime genres (Mecha/Magical Girl) and focus around messed up kids going insane.
If you liked
Code Geass: Hangyaku no Lelouch
|
...then you might like
Angel Beats!
|
Though KEY and Sunrise are two very different Studios, Code Geass and Angel Beats are similar in several ways. Both focus on a teen resistance group trying to defeat a force much more powerful than them, and both have that sort of bittersweet feeling that makes you happy and sad at the same time.
If you liked
Elfen Lied
|
...then you might like
Higurashi no Naku Koro ni
|
Both involve cute, shoujo-ish teenage girls violently tearing eachother to pieces. If you think you were "hardcore" enough to watch Elfen Lied, you just might be hardcore enough to watch Higurashi.
If you liked
Elfen Lied
|
...then you might like
Highschool of the Dead
|
Both are action-type animes with a tiny bit of comedy, have slight harem themes, and involve lots and lots of killing. Also, great dubs. To sum it all up in one sentence: boobs, blood and death.