This is my first go to place when I am looking for an online course that are truly taught by experts in their fields. The best part is that it is free of cost. The courses are challenging and you will learn a lot if you do their exercises and homeworks. Below is the description of EdX taken verbatim from their website:
EdX offers interactive online classes and MOOCs from the world’s best universities, colleges and organizations. Online courses from MITx, HarvardX, BerkeleyX, UTx and many other universities can be taken here. Topics include biology, business, chemistry, computer science, economics, finance, electronics, engineering, food and nutrition, history, humanities, law, literature, math, medicine, music, philosophy, physics, science, statistics and more. EdX is a non-profit online initiative created by founding partners Harvard and MIT.
Coursera is another option that you should check for online courses. They are equally good as edX and they are free as well. If you can’t find a course in EdX, its likely that you will find it in Coursera. Please keep in mind that you may find many courses of overlapping topics between EdX and Coursera. At the time of this writing, Coursera is also available in Android and iOS devices.
While the aforementioned resources are highly academic and is very helpful in strengthening your foundation, the following resources also come highly recommended especially for enhancing certain skills like learning a programming language, Microsoft Excel, digital photography, language, cooking, preparing for a certification like CCNA, GRE/GMAT etc., Check out the following websites and see what you think:
If you know of other helpful online resources that you may find fit to add to this list then please contribute by adding those in the comments.