Who is the singer for the vampire knight opening song?

The song isn't actually called Vampire Knight. If you are referring to the first season it's called Futatsu No Kodou To Akai Tsumi by the band ON/OFF. Sadly you won't find it on iTunes but I got it at this website gendou.com . But if you are referring to the second season I believe it's called Rinne Rondo by the same band. And you can get it off the same website.