Video Resources for Teaching Middle-School Science

My sister, who is a science teacher, is having trouble finding quality videos for middle-school-aged students (grades 5-7). The last video she ordered turned out to be geared more towards grade 1 kids. Some of the topics they're covering right now include changes of state and components of mixtures and solutions. If you know of anything good related to these, or any other topics in chemistry or biology (that she can have on hand for substitutes on sick days) and have info on where to order it, please leave a comment in this blog space for her and any others in this predicament.