Hardware Sample Test: http://www.proprofs.com/certification/comptia/a-plus/exams/HW-E1/exam.shtml

OS Technologies: http://www.proprofs.com/certification/comptia/a-plus/exams/OS-E1/exam.shtml

General practise tests: http://www.pc-technician.net/quiz.aspx

A video about the CompTIA exam: https://www.youtube.com/watch?v=Nq9LnfAkOcM#t=64