I've said this before, but this year has really been one of our best. I do think it's in large part to us moving to a more self directed learning style.
To pull books for my kids to read for history, science and literature I use a few sources. I pick and choose based on what books are easy to obtain. I prefer in hand books verses reading on the computer, so that factors in for me as well.
The book lists I use are:
-Old Fashioned Education
-Robinson curriculum list 1
-Robinson curriculum list 2
-Robinson curriculum list 3
There are also some premade schedules on the Robinson yahoo loop for grades K-12.
And this blog has great info.