Math Antics Fraction Videos - Not just videos! Lots of resources here...for a great Abbot and Costello video on multiplication (yes, I'm serious) look under the video picture and click on grade 4, then go to the bottom of that page where the video picture reappears, and click on #2 under the picture. It's the perfect video to discuss mathematical thinking!
Story of the World video links. Very well-organized by book and chapter in SOTW, with the videos imbedded onto the page (i.e. no second page click to go to YouTube). Most of the clips are just a few minutes long too, so good for a quick reference.