Dr. Sears' "THe Baby Book" has an excellent month-by-month guide of milestones for all sorts of skills and abilities, and the chapters on development have great recomendations about what you can do with your baby at each age and what sorts of things they would find amusing. I recommend it highly and have used it often. It's also good for troublshooting sicky symptoms and is very pro-nursing and AP. Pricey, but worth it!