1. Brainpop. The kids love the silly little characters Tim and Moby. The topics are relevant to the 3-7th grade curriculums. The video is short and to the point (2-3 minutes) and reviews essential vocabulary. At the end, you can use the interactive review quiz, which works great with the smart board or mimeo technology. (They do offer a free 5-day trial and some free stuff if you aren't up for the $195 fee.)
Math-related episode clips (rather than the full episode) can be downloaded for free at Teacher's Domain, AND, even better they come with a list of correlating state standards, related worksheets, and lesson plans. Check out a full list of episodes as well as correlating NCTM standards over here at PBS' parent page.
(Check out one of my favorite clips: here. It is a clip from the end of the episode's "For Real" feature.)
3. Any and all games/activities that are interactive with the SMART board. As for ALL my favorite math resources, I try to keep track of them over here at my delicious account. (But as you can see, I haven't gotten the hang of tagging and organizing links ...so this is a work in progress. ) Check one out from BBC below!