Some of you may be familiar with the "Ted Talks" series, which is a collection of talks and presentations from people in various fields. These talks are often very engaging or cutting edge, and often create good places to start discussion.
Ted-Ed is a subset of these talks, and what makes them great is that they've been animated. These are more engaging to students. Further, each of the videos in Ted-Ed contains some good supplementary materials in the forms of post-viewing quizzes and discussion questions. The creators of this website have created a turn-key solution to flipping; if you do not have the time or expertise to create your own videos, you can use the ones on Ted-Ed and you can assess student comprehension via the quizzes and discussion material.
Currently there are a limited amount of videos, and many are not subject-specific, but focus on broader ideas. These are definitely a nice way to access the meta-structures of learning and to open up interdisciplinary discussions.
I highly recommend this site as a supplement or introduction to your own flipping adventures.