Yuno Gasai Mirai Nikki
The epitome of crazy stalker girl.
Pretty much every girl in Higurashi no Naku Koro ni
This one might be too old for most of you.
Anna from Shimoneta to Iu Gainen ga Sonzai Shinai Taikutsu na Sekai
Well this is my favorite crazy stalker person, plus they are a vampire!
Megumi Shimizu from the show Shiki
Kaneki, he is an attempted case of secretly crazy.
Tough choice but I want to say Tokisaki Kurumi.