This is primarily for public/private school teachers. However, if you sign up, they will email you a list of ebooks for free every week that you can download and use. They are written by teachers, and when they're not free, they usually cost reasonably little. All subjects, all grade levels.
Thanks for sharing this site...I just started looking at it, but it seems like they have a lot to offer!
I've been using this website for quite awhile now. I work as a nanny, I've used lots of the free items and purchased items off this site quite a lot for work. There is something here for everyone.