I just found the first three ending theme songs for movie #1 to #3, all composed by Kajiura Yuki and sung by a new artist, the band is named Kalafina. Her first album with the three songs will be called "Oblivious" and will be released on 1/23/08. There are small samples for all 3 songs at her
official web site.
Sounds good! She mentions on her blog that all 7 ending themes will be sung by Kalafina.