In an earlier post we mentioned KhanAcademy.org, which has thousands of short video clips covering math, physics, chemistry, history, and more. In addition to the videos you will find short self-assessments.
iTunes U by Apple, offers free lecture videos from big universities (Stanford, Arizona State University, Texas A&M, and more). Download the free iTunes application, then search for an area of interest and see the offered courses. While the courses include long videos, they are first downloaded to your computer/iPad/iPhone or other Apple device, so that you can then watch them offline.
For advanced topics related to computer science, see the courses by Stanford University, University of Michigan, and UC Berkeley offered through coursera.org. These courses are rich in short videos and interactive and self-assessment learning activities.