These are the sites that I usually use when preparing for lessons
Website: http://www.youtube.com/teachers
Website: http://sites.google.com/
Paid iPad app: https://itunes.apple.com/us/app/wikinodes/id433834594?mt=8&uo=4&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.zondle.mobile
Free iPad app: https://itunes.apple.com/us/app/zondle/id497342127?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/zondle/id497342127?mt=8&uo=4&at=10l6SU
Website: http://www.zondle.com/
Edmodo app: http://www.edmodo.com/publisher/zondle
Website: http://www.sharemylesson.com/