We really found the following books extremely helpful.
1. "Sleeping Through the Night: How Infants, Toddlers, and Their Parents Can Get a Good Night's Sleep" by Jodi Mindell, PhD. This one helped us understand differences between infant and adult sleep patterns. Based on actual research conducted by the author.
2. "On Becoming Baby Wise" by Gary Ezzo. This was really helpful by its suggested schedule and sleep strategies. We did not use everything from this books, but we picked and choose what tips worked best with our family. There is also a blog, "Chronicles of a Baby Wise Mom" that was extremely helpful when I was implementing some of the suggestions and needed feedback from other mom's using Baby Wise or just wanted to read about other Baby Wise mom's experiences. http://www.babywisemom.com/p/blog-index.html
We also read "Healthy Sleep Habits, Happy Child" and "Baby Whisperer" but those are already mentioned above.