Study Jams is a resource provided by Scholastic that covers a multitude of elementary mathematics and science topics. It has a variety of resources that consist of videos, interactive activities, and karaoke. I would highly recommend it as a resource for introducing or reviewing topics as it focuses heavily on key vocabulary for each skill.
Here is the drawback, it is built on flash. What does that mean? It will not work on iOS devices. So the solution for the elementary teachers I work with would be to just use it in a whole class setting or use it in the computer lab. You could also use some of the songs and videos as a transitional period between subjects. A great way to make this happen would be to create your own Symbaloo page. Zack gives some fine directions on making your own Symbaloo page here. By making your own Symbaloo page, you can link specific examples all on one website because you may not want to use all the resources listed. This would allow you to quickly pull up the specific resource you want.
Check out Study Jams. I think you will be pleased with amount of quality resources that are there.