I may be a bit biased toward this one since I helped fund it. If you consider yourself a lifelong learner, you have to check out the Big History Project.

One of my favorite sources for interesting lectures is The Teaching Company. They get incredible professors to teach courses on pretty much every topic you can think of.

I think everyone could benefit from learning how to write even some basic code. Even if you don’t use it in your day-to-day life, computer science forces you to think abstractly and solve concrete problems. Code.org is a terrific resource for learners of any skill level

Khan Academy’s short videos are a great way to get smarter in just a couple minutes. My kids have used them for their classes, and I use them to refresh concepts that I haven’t studied since high school. Their videos are a tremendous resource on topics ranging from basic arithmetic to complicated subjects like electrical engineering.