Kip's Practice FAA Knowledge Tests.
[LINK] Kip's FAA Written Test Preparation Page for "Knowledge Exam. Many options including Commercial, CFI, Sport Pilot, Glider, more! [Updated 1 Nov 2007]
Private and Instrument Tests from Risingup.com.
[LINK] Practice test by random or by selected subjects.
Aviation Instructor‘s Handbook Quiz.
[LINK] A simple if clunky page to test your understanding of Fundamentals Of Instruction from the Aviation Instructor‘s Handbook.