Anneberg Media's Learner.org site is a collection of curriculum resources for all subject areas, and sorted by subject and grade. Grade level areas are K-4, 5-8, 9-12, and College/Adult.
The resources include lesson plans, on demand free videos, and links to DVDs and other materials that can be ordered for a fee.
The free on-demand videos are great for enhancing your curriculum or lesson with short video clips that can engage your students while explaining or exploring a concept.
There are also resources for teachers for professional development and training.
Many of the video clips are from public broadcasting programs. The free videos are a great resource for any teacher.