The official CLEP book from CollegeBoard is a good investment. My sons have found the REA books w/CD to be helpful, too.
My older son is trying to finish his AA this year. He took 17 credits at the community college and 12 credits in CLEP last semester. It was doable. He didn't seem overworked or stressed. He clep'd Sociology, Psychology, and American Literature.
Watch out for CLEP in any science classes. Usually, these are allowed only 3 credits because they do not include any lab experience. Our college requires 8 credits of science and they won't accept chemistry or biology CLEP at all unless a student successfully passes a lab science course at their school. Check your school's policies carefully. Talk to an advisor about your plan.
Here is a site with resources for study: Office Solutions - Accelerated CLEP Study