Study Jams

Produced by Scholastics, this site gives many definitions in science and math.  There are videos, slide shows, and step by step instructions to many terms and procedures.

http://studyjams.scholastic.com/studyjams/index.htm

WatchKnowLearn has indexed over 33,000+ educational videos, placing them into a directory of over 3,000 categories. The videos are available without any registration or fees to teachers in the classroom and to students at home 24/7. Users can dive into our innovative directory or search for videos by subject and age level. Video titles, descriptions, age level information, and ratings are all edited for usefulness.  

http://www.watchknowlearn.org/