Okay...as I mentioned before, Kalafina is awesome. I posted a few songs to check out earlier.
Other than that, some of my favorites:
Asian Kung-Fu Generation - Rewrite
Asian Kung-Fu Generation - Maigoinu to Ame no Beat
Claris - Connect
Claris - Irony
Claris - Naisho no Hanashi
Coaltar of the Deepers - Dear Future
Etsuko Yakushimaru - Nornir
Etsuko Yakushimaru - Boys, Come Back To Me
Eiko Shimamiya - Higurashi no Naku Koro Ni
Eiko Shimamiya - Naraku no Hana
Eiko Shimamiya - Superscription of Data
Faylan - Dead End
FictionJunction - Stone Cold
Galneryus - Alsatia
Galneryus - Cause Disarray
Iori Nomizu - Ma-Ka-Se-Te Tonight
Kanako Itou - Hacking to the Gate
Kanako Itou - F.D.D.
Kanako Itou - Find the Blue
Kana Hanazawa - Ren'ai Circulation
Lisa - Oath Sign
Mami Kawada - PSI-Missing
Mami Kawada - Masterpiece
Mami Kawada - No Buts!
Mami Kawada - See Visions
NICO Touches the Walls - Hologram
NICO Touches the Walls - Matryoshka
Kenji Ootsuki - Hito Toshite Jiku ga Bureteiru
Kenji Ootsuki - Kuusou Rumba
Kenji Ootsuki - Ringo Mogire Beam
Kenji Ootsuki - Zetsubou Yuugi
Rookiez is Punk'd - Complication
Rookiez is Punk'd - In My World
School Food Punishment - How to Go
Shihoko Hirata - Key Plus Words
Shoko Nakagawa - Sorairo Days
SID - Rain
supercell - Kimi no Shiranai Monogatari
Sachi Tainaka - Disillusion
Theatre Brook - Uragiri no Yuuyake
UVERworld - Core Pride
Yousei Teikoku - Kuusou Mesorogiwi
Yousei Teikoku - Filament
Yui Horie - Sugar Sweet Nightmare
There you go plenty of music to look into