United Streaming.com is a great resource for both homeschooled and traditionally schooled children. It is subscription based program that is free in GA, LA, SC, IA, AR and RI, because the State education departments have already paid for it. If it is not free in your state, is may be free in your school district, so check before you purchase a subscription. Homeschoolers can also purchase the subscription for $199.00 a year. Schools pay a license fee of $500.00 or more.
The website describes itself as “a digital video-on-demand” service with more that “4,000 educational videos available for use in the classroom-at any time you wish””
The site is designed for teachers to use, with a new site (costing $10.00 a month or $100.00 a year in the beta phase) that is designed for children to use on their own. It is great to use when there is a concept that a child needs extra instruction in, but I have had it for months and have not used it regularly. (We already have a full work load.) It is not very user friendly and written for in teacher-ease which can be inconvenient for parents. You may take the online tutorials to help you utilize the system better.
If your child has time and the initiative to explore the videos on this site according to interest, I would say it was a valuable investment. He or she can explore any subject matter they wish from percentages to pyramids and more. If they already have a full curriculum, they may end up not using it very often, and, some of the movies can be long.
If the site is available to you free, then go for it! If it is not free, and your child takes initiative to learn on its own, then I recommend it as well.
Just about every subject is covered in this online curriculum aid.