With all of the math and computer science concepts taught by Khan Academy, I was surprised to discover that there's no materials on truth tables.  I'm taking a class about logic and probability, and that's something that we are focusing on right now, but the course materials are very lacking, especially in exercises.  I was hoping to find help on Khan Academy, but can't find anything here, and scraping through Google searches hasn't helped either on several of the concepts.  Would love to see help in this area!