"The National Library of Virtual Manipulatives" (Software package promoted for sale, but they also have a free version. Very nice site chock full of online applets and manipulatives for teaching math concepts to students of all ages. ALL the online manipulatives – and there are HUNDREDS of them – are free. http://nlvm.usu.edu/en/nav/vlibrary.html
Digital History University of Houston has #homeschool history assignments, projects, primary source documents, textbook, an options for "light" or "in depth" study. Free, but the worldview may not fit all families.
TeacherLINK, an online teacher resource for educators and students, is provided as a free public service by Utah State Universitys Adele and Dale Young Education Technology Center (the YETC) and Emma Eccles Jones College of Education and Human Services.