ACT
www.ACT.org has best information for ACT along with practice tests and prep help from Princeton Review.
SAT
www.collegeboard.com has partnered with KHAN Academy and have free prep help for the SAT/PSAT.
* Guidance has paper practice tests for ACT/SAT as well - just ask!
ASVAB
PERT
http://www.mometrix.com/academy/pert-test/
https://uniontestprep.com/pert/practice-test
PSAT
https://collegereadiness.collegeboard.org/psat-nmsqt-psat-10/practice/full-length-practice-test
AP Exams
https://apstudent.collegeboard.org/takingtheexam/preparing-for-exams
http://www.appracticeexams.com/