The internet is one of the greatest resources available to mankind. But it's not just Google, YouTube, and cat photos. There are tonnes of free resources that can help you, both in self-improvement and in entertaining oneself. Here are the ones we like:
Books are food for the mind. Reading good books is always a good habit and now you can read for free, so there's no excuse not to. Not that normal libraries are expensive, but a digital library means you can read in the comfort of your own home. Plus, if you have an e-reader, you can carry around an entire library without straining your back.
Project Gutenberg is a digital library. One can simply go to their website, search for a book and download it. Formats include plain text and kindle compatible versions. The books here are all public domain or reproduced with permission, so there is no guilt involved with reading the books for free. And with the convenience of the internet, you can easily catch up on reading some old classics.
If books are too boring, how about a good film? If you enjoying learning about a particular topic, then take a look here.
With documentaries from categories such as science, history, war and many others, this site is one of the larger sites for documentary content. So, if you're interested in watching something on the making of Inception, or the pyramids, or maybe J.K. Rowling, go take a look.
Learning from other people is how education generally works. Listening to people talk can be an enlightening experience and better than any book - depending on the speaker of course. Here is a site with some of the most interesting speakers around.
Technology, Entertainment, Design. Perhaps the most famous set of conferences out there right now. So successful that is spawned a spin off branch in the form of TEDx. TED talk speakers have something insightful to say, and are given less than 20 minutes to say it. The list of speakers is filled with luminaries such as Google founders Larry Page and Sergey Brin, Bill Gates, and many Nobel Prize winners. That's right, "many" Nobel prize winners, so you know there are some big shots speaking at TED.
You like maths? You like figuring stuff out? Or do you just want to get a quick answer to a mathematical question? Wolfram Alpha can handle it.
Probably one of the most boring, yet mundanely useful resources on this list. The famous online calculator or "answer engine" can provide answers to simple questions, such as dice roll probabilities, feet to metres or gallons to litres unit conversions, but it can also handle the complex mathematical problems one might encounter while studying calculus. It might not be so entertaining, but it's worth keeping this one in mind.
University Coursework and Lectures
Open sourcing. Improving educational access. Knowledge sharing. Universities across the world are not just talking-the-talk but walking-the-walk, and uploading their course materials to the web for all to see. This might not get you your PhD, but it's a pretty good place to start.
Covering topics ranging from Classics to Economics to Physics, these university resources are good reading and listening material for the curious. If you are interested in academia, then Yale and MIT have open coursework available to the public.