I recently purchased the book 'Beyond the body' by Susan J Blackmore, and can highly recommend it. The book is very readable with a good style.
I have read most of the literature available on the subject including the early classics, but this is the most thorough and unbiased investigation into OBEs or Astral Projection that I have come across. Ms Blackmore quotes from all the important sources on the subject and gives details of all the experiments which have taken place from the 1900s onwards.
This is a must read for any serious student of the subject.