The internet is filled with free educational lectures, and many of those lectures are spread across a variety of platforms, from free university sites to YouTube. FindLectures attempts to provide a single place to search through them.
Right now, FindLectures has catalogued around 36,000 lectures across various categories. The sources come from a broad range of places, with Oxford University and the Library of Congress making appearances. Just type in a search string and you can filter the results by collections, speakers and categories. When you find what you're looking for, FindLectures links you off-site to wherever the video or audio file is originally hosted. You can even turn those results into a podcast RSS feed so you can catch up with them no matter where you're at. The content is all curated too, and generally seeks to prioritise experts and primary sources wherever possible.
It takes a little while to find exactly what you're looking for on FindLectures, but if you search in broad strokes and have some time to dig around, you'll find some great lectures here.