MIT Opencourseware provides online courses as taught by MIT instructors. The content available within the courses varies: some of the courses just have syllabi, while others have audio lectures with transcriptions, problem sets and exams, and solutions manuals, as well as free online books. If you're interested in a particular topic, or just want to browse, this is a great place to start.

Coursera hosts a wide variety of courses in a wide variety of languages. You can often choose whether to take the course for free, which might mean that you're restricted to a certain timeframe to complete your learning, or to pay $50 for a certificate once you're finished and permanent access to the course materials.

EdX houses online courses hosted by Harvard and MIT, among others. If you're interested in learning it, chances are good that EdX has it.

IMF Online: The previous links give courses in just about any topic you could want. If you're interested in training more directly relevant to your work, the IMF online courses are likely a good source.

The World Bank Open Learning Campus (OLC) has an array of online courses in development-related topics. It's a good place to look if you're looking to gain a little more knowledge in your area, but are stuck at home and can't get away for in-person courses.

Marginal Revolution University, founded by Georgetown professors Tyler Cowen and Alex Tabarrok, is a completely free online resource for economics courses. The videos are all downloadable, and cover more recent research than many more traditional economics courses might.

For a quirky blog that applies economics to everything, check out their blog, Marginal Revolution.