RHCSA/RHEL Books and Sites

Books:

RHCE Red Hat Certified Engineer Linux Study Guide (Exam RH302) (Certification Press)

Red Hat® Certified Technician & Engineer (RHCT and RHCE) Training Guide and Administrator's Referrence

Foundations of CentOS Linux: Enterprise Linux On the Cheap

Hands-on Guide to the Red Hat® Exams: RHCSA™ and RHCE® Cert Guide and Lab Manual (Certification Guide)

Sites

RHEL 6 SRPMS
RHCSA Tutorial Notes

Blogs 

System Admins Kodigo for RHCSA
Linux Superuser