For Preschool, I use World Book's Scope and Sequence to help me know what my children need to learn. I also use Slow and Steady, Get Me Ready and How to Teach Your Child to Read in 100 Easy Lessons.
But, this morning I found a great site via a friend's blog that seems to have just about everything you'd need to teach your child preschool at home for free. Here's the site: http://www.hubbardscupboard.org. Happy Preschooling!