Here is what our good friends (both are scientists and are currently sailing around the world with their son) wrote on homeschooling materials. They have very high standards. I found it very interesting:
In our ongoing quest to find good homeschooling materials for our son, we have discovered two online sites with free courses that we really like (an understatement). One is called "HippoCampus". Our son has started using the AP Biology and it is wonderful. It is so good, in fact, that we recently switched his science and history courses from another for-pay course site (BYU -- very underwhelming) to this one.
With both of the HippoCampus courses I want do as much side-by-side learning, or eavesdropping, with him as I can. These are not a stand-alone courses; most students would need a teacher or parent to supplement the presentations, but the materials are top-notch and would also help any student who was in a traditional or weak course.
The other online course site is the Khan Academy. It is an amazing collection of free lectures in math and science. They recently have added an "exercise dashboard" for the math series, set up to feel a bit like a game with your effort and progress tallied visually and broadly with a point system. Our son and his friend in Arkansas are now both using it and comparing notes on where they are. The Khan Academy materials would be helpful for students from middle school the college level. Check it out. It is totally free.
http://www.khanacademy.org/
I am a taken aback by the realization that my assumptions that "you get what you pay for" are not holding up in the realm of online educational materials. BYU's courses each cost $126, but the two we have tried have been very weak -- as if they have not been updated in years or a decade. Also, their promised instructor feedback is embarrassingly poor. In fact, we are asking for 2 refunds from BYU and moving on to these much better free sites. HippoCampus and the Khan Academy are enriching our son's studies of US History, Biology, and Math. He is also enjoying the Teaching Textbooks Algebra program and connecting with far away friends using Google's video chatting tools.