Very well made making of documentation for Angel Beats! anime. The recording of the OP/ED by Lia and Aoi Tada including comments by both singers and Jun Maeda. Interviews and more.
Angel Beats! (エンジェルビーツ!) The Making Episode 1&2
Appears on these pages
https://www.youtube.com/watch?v=izGJdIiuq_I I AM DESPERATE FOR A SUBTITLE.