Edmodo: http://www.edmodo.com/An excellent educational and social platform
Flipboard: https://play.google.com/store/apps/details?id=flipboard.appFlipboard brings together world news and social news in a beautiful magazine designed for your Android phone and tablet.
Glogster: http://www.glogster.com/Create lovely interactive, multi media posters
How Stuff Works: http://www.howstuffworks.com/Reference site for all subjects including technology
Image Chef: http://www.imagechef.com/Add fun effects to your images, and create interesting visuals for presentations
Jigsaw Planet: http://www.jigsawplanet.com/Easy to use online jigsaw puzzle game. Can be embedded onto blogs or wikis.
Karaoke Party: http://www.karaokeparty.com/Fun and easy online karaoke
Listen a Minute: http://www.listenaminute.com/Excellent online listening site created by Sean Banville