There is a sort of hidden feature in YouTube where you questions to a YouTube video that you created or uploaded.  It is a beta feature but if you go to www.youtube.com/testtube, you can add it to your account and insert questions into videos.  These questions will stop the video and either, depending on the option you select, keep it paused till they answer it correctly or just until they answer it.  This could be a great way to help students check their understanding during various parts of a video or a way for you to get feedback, like a poll, from the viewers.  You are restricted to multiple choice questions but there is still information you can get from students or others using those types of questions.