The following resources can be used in a variety of subject matters. In addition, you have a link to "The Best of the Best Websites" which has a mixture of awesome sites to visit.
Annenberg Leaner www.learner.org
ClassTools www.classtools.net
Kahoot www.kahoot.com
Powtoon www.powtoon.com
Padlet www.padlet.com
Thing Link www.thinglink.com