QuizSlides is a service whose purpose is to help you build quizzes based upon your slides. I reviewed the service back in May of 2012 when it was in beta. Today, QuizSlides sent out an email announcing that they are removing the beta label. Along with that announcement was the news that QuizSlides will be a fee-based service starting in 2014. You can continue to use the service for the rest of 2013 for free.
QuizSlides allows you to upload PPT or PPTX files containing questions then add answer choices to create an instant-feedback quiz. The quiz can be set to allow students to try answers until they get the correct answer or the quiz can be set to allow only one try per question.