Need an environment for students to share and collaborate outside the classroom? Try Piazza. You can create an environment for each class and limit participation. Take a look at the stories about how others have used Piazza. Then "take a tour" to see how easy it is to setup and use.
Marketed as the "zooming presentation editor," Prezi is a great presentation tool that can help you focus on concepts rather than the linearization of PowerPoint. There is also an iPad app where one can control the presentation using multitouch gestures.