1. https://www.coursera.org/ - Collection of great online video lectures
2. NPTEL website - Video lectures from different IITs and IISc (currently their official website is down but their youtube channels are there)
3. https://www.quora.com/ - Quora, a question answer website for increasing general knowledge, entertainment
4.http://www.passhojao.com/ - To get solved and unsolved previous years question papers of ISC/ICSE board , interactive forum to ask questions. Recently college semester exam papers are also being added. Not much websites for school students you see!
5.http://www.jeequery.com/ - Question answer platform for preparing for engineeing entrance exams with active responders. Here you are :D