Socrative is a free web-based student response system (with an app now too). Get instant feedback about what students know about a topic. Eliminates the need for expensive hand-helds. Allows teachers to create quizzes, polls, and exit tickets. Can be used in “real time” by students who each have an iPod Touch/iPad or laptop, or by students rotating through one computer in a classroom center or at home.
Great site with tons of iPad apps for the classroom (and ways you can use it even if you only have ONE iPad). I use my iPad with my classes a lot. Tons of great apps (I use it with my Kindergarten kids)