I don’t know how many people know about this, but McGraw-Hill and Glencoe (makers of most of the school textbooks) have some great interactive online resources. For a free resource from a major textbook company, they are absolutely wonderful.
I also found this from Orange County, Florida. I have to say they have more resources online than I can find in any other school district I’ve looked for. Not that I can’t find tons of resources, but this is something with the school district’s mark on it.