I bought Baby 411 used, and it paid for itself the first night our infant would NOT stop crying. They have a list of things to try to get your child to calm down, and we used most of them that night. That page is bookmarked, because what works one night is guaranteed not to work the next time
We do have other books that were gifts, including one our pediatrician recommended. Baby 411 is the thinnest, so it's easier to hold at the same time you are holding your child, and you don't have to flip as many pages to find what you need.
Happy Healthy and Handsome DS 8/13