Free Online Practice Exams

• Aplus Omega
  About 200 practice questions online.
• BrainBench
  BrainBench has some free tests. Look for "Computer Technical Support" or something similar. Otherwise, they offer a certificate for passing their exams, which only cost about $20 each. Free registration required.
• BrainBuzz Skill Drill
  Another online test that also provides a certification if you pass. This is probably one of the most difficult I have tried. Registration required.
• Exam Cram
  Site by folks who publish ExamCram books (Coriolis). Requires free registration.
• FreePractice.com
  Has a number of tests, automatically graded. Annoying banner ads.
• LearnThat
  Tutorial and a test. Partnered with FreePractice.com.
• William Dean Practice Tests
  Eight tests automatically graded and one crossword puzzle.