Worksheets by grade. just click the worksheets tab at the top of the page. So handy for combating that summer brain drain! I think the kids and I will incorporate a "School Day" one day a week this summer :)
PAID printable but has a neat test maker and lots of different worksheets year math, ELA, science, social studies, and seasonal tests/worksheets with an option to administer tests online (with auto-grading).
Books by the Foot. Each box contains approximately 150 books (give or take). You can also order more age/grade specific books, but it costs a bit more. There is now an advisory on their site that due to high demand, boxes may not ship for up to 5 weeks.