There are really too many I like to pick a favorite but.. the first one that comes to mind is Discotheque by Mizuki Nana. That opening was half the reason I got through Rosario Vampire.
~ Genei Wo Kakeru Taiyou (LiSA - traumerei) ~ Little Busters! ~Refrain~ (Suzuyu - Boys Be Smile) ~ Little Busters! (Rita - Little Busters!) ~ Shugo Chara! Doki! OP.3 (Guardian 4 - Omakase Guardian) ~ Black Rock Shooter (supercell ft. Hatsune Miku - Black Rock Shooter)
Hyouka- Yasashisa no Riyuu Sword Art Online- Crossing Field Tokyo Ravens- X-encounter To Aru Kagaku no Railgun- Judgelight Sket Dance- Kakko Warui I love you! Yumekui Merry- Daydream Syndrome All Shakugan no Shana Op's All D Gray Man Op's
OP song of Umineko no Naku Koro ni, Katayori no Tori (i think o.o" i kinda forgot the spelling) by Akiko Shikata and all the OP songs of the Umineko visual novels.
Kuroshitsuji : Monochrome Kiss (SID) Soul Eater: Paper Moon (Tommy Heavenly6) Full Metal Alchemist: Period (Chemistry) Rewrite (Asian Kung-Fu Generation)
Higurashi no naku koro ni kaku , L'attaque des titans , Toaru Kagaku no Railgun , Que Sa Volonte Soit Faite , Mondaiji tachi ga isekai kara sou desu yo, SAO Fairy tail ...