I came across a very interesting paper entitled The Thermodynamics of Black Holes by Robert M. Wald, 2001, at the following link:
http://relativity.livingreviews.org/Articles/lrr-2001-6/

This contains a lot of information of interest to me including a review of approached to calculating entropy for black holes. It also includes a references to joint papers with Unruh. I need to come back to this when I have time.