When I was researching international adoption, The Complete Book of International Adoption was my favorite book and the one I still use often.  The author takes a complicated subject and breaks it down into clear and concise topics.  It helped me decide which agency I would choose, and has a questionnaire that helped both me and my husband identify which issues were important to us in adopting.  There is also detailed info about all the countries that have programs, and the author has a website where she lists new updates.