Study Jams: TONS of free and fabulous content for math and science at the elementary level. Students and teachers can select the subject area and then view a treasure trove of related content. You have access to vast amounts of high quality and high engaging videos, step-by-step slides, and fun quizzes. Many of the concepts even include fun songs the students can sing along with in a karaoke style fashion. Way to tap into those multiple intelligences!
Scholastic has created a site called StudyJams!, full of over 200 short, upbeat educational videos on math & science topics. The videos are organized by topic, so you can just find the video that matches the educational concept you're covering in class!