CosmoLearning is a platform where anyone can access free video lectures from the University of Houston. Subjects are wide-ranging and as diverse as 'Development of the Novel' to 'Darwin's Legacy'.
You may already have heard of the Khan Academy which is based on the same principle, although the academy focuses on the areas of Math, Science and Humanities. The material on this site is probably more suitable for high school learners although some of it is undoubtedly beyond the level expected in an average school.
Or how about some courses from top-class educators from the likes of Yale, Harvard and Princeton? Academic Earth offers such courses for those who are just looking to touch up their knowledge of a particular area, but also provide (presumably paid) courses for credit from Bachelors to Masters.
All these sites offer high quality materials for anyone to further their knowledge in their area of interest so it's worth browsing to see how you could use them to supplement your own teaching and learning.