I read Documents of the Christian Church (selected and edited by Henry Bettenson) for seminary. Sometimes dry byt sometimes very interesting.

Hildegardt is good,

And the Niebuhr brothers (Reinhold and ?). They wrote in the first half of the 1900s about social change.

Jung is also good, but a tough read, so most people read someone else's interpretation of Jung.

The Early Years of Jesus Revealed is an interesting one, speculating that Jesus was schooled as a gnostic, then returned to Judaism with some gnostic wisdom. (Oops, I can't find that on amazon, so maybe I'm remembering the name wrong. I'll check my bookshelf.)

I also like Social Teaching in the Episcopal Church by Robert E. Hood.