Items 1 thru 3 on this page are the study materials directly from the FAA. They will prepare you for the FAA knowledge test to obtain your Part 107 drone certificate.
Item 4 will bring you to the FAA Youtube Channel. These videos are awesome for learning about airspace and safety.
Items 5 & 6 include some more great information in regards to drone operations and safety.
oRemote Pilot Study Guide
How to read a sectional chart
Pilots Handbook of Aeronautical Knowledge
FAA Webinars for drone pilots (Awesome videos for Drone pilots)
Introduction to Part 107 rules, etc. Provided by AOPA
Best Practices when it comes to Drones & Privacy