Edmodo - great way to communicate, grade, make quizzes, and much more

Fantastic tool for teachers.  Grades quizzes and tests for you, unlike Google forms where you have to take a few steps to grade things.  Easy for kids to recognize due to Facebook-type look.

www.edmodo.com

Instant feedback in class via phone or computer

Great for getting quick feedback on presentations, etc.

http://www.polleverywhere.com/