QUIZ your students to see how much they have learned when watching a YouTube video, using Ted Ed, Blubbr or Teachem quiz makers.
Use Stu's Quiz boxes to create a Jeopardy-style game.  Use Classtools.net to create games and quizzes - your students can use this site too.
POLL your students, using Forms [perhaps with Flubaroo]  in Google Drive, Survey Monkey [Example] or live polling with Socrative