There is so much power in videos. They are meant to supplement curriculum, enrich curriculum, reinforce curriculum, reteach curriculum and take learning to the next level. Following are some of my favorite videos sites:
YouTube: One can subscribe to several existing channels. If you don't like the existing videos, go ahead and create one, upload it to YouTube. Share it with your students, colleagues. Since we have Google Apps for Education at our district, YouTube is linked directly to the account. Here was an article yesterday on some Science channels on YouTube. It is all free of course. Just got this from a friend: How to make your YouTube videos interactive.
Vimeo: This lesser known sometimes (compared to YouTube) website also has a wide range of videos. Again, you can create an account and upload your own videos here.
Ted and Ted-Ed: Two of my favorite websites because of the amount of learning that can happen with them. On Ted Ed, you can take a lesson and flip it. The length of the videos is just right, even for a kindergarten class.
At our district we also have subscriptions to BrainPOP (an all time favorite with all elementary age groups), BrainPOP Jr (the primary age version), BrainPOP ESL (for English Language Learners) and Safari Montage.