Aside from tons of Google and YouTube I used very few resources to study and pass the Security+ certification exam. Here is that list . . .
CompTIA Security+ Get Certified Get Ahead: SY0-501 Study Guide– For me the Darril Gibson book was all I needed to read, as far as books go. Easy to read, concise and more than adequate to get the job done.
Professor Messer– Messer is simply a genius! He breaks down everything you need to know in the most straight forward manner and just deep enough to take you in depth but not TOO in depth. Some of his course materials cost $ but you can find plenty of his videos free on YouTube as well.
COMPTIA Certmaster – Because I paid for a retake voucher as insurance I was able to access a bank of Certmaster questions that I found VERY challenging and VERY useful. Their questions take it up a notch, which puts you in a good position to do better on the exam.