When I read this post, I was reminded of a book I read by Brian Weiss called Same Soul, Many Bodies.
He basically hypnotized people to do regressions/progressions, and found that he could regress them to a certain period before they were incarnated as human beings. He talks about things like the incarnation process where spirits choose the circumstances they want to incarnate based on the growth they want to achieve in that lifetime. He also progressed people into the future (or some of many possible futures anyway), and he has stories of new technologies and human evolution and stuff.
Another person who also does the same kind of therapy and discusses the period 'in between lives' is Michael Newton. You can try listening to an interview of him from the
Theatre of the Mind podcast. It's the November 28, 2006 show. Really interesting stuff.