For elementary and middle school we are going through the "Dorling Kindersley Science Encyclopedia". This book covers just about everything from atoms to space to weather to biology. And every page is packed with wonderful color pictures. At $40, it seems expensive. But considering we paid almost $100 for the Oak Meadow Science syllabus which covered only 80 of the 400+ pages in the Science Encyclopedia, it turned out to be a really cost effective resource. This book will take a couple of years to get through even at the rate my kids eat it up.
The Hirsch books are also wonderful -- although I didn't get some of this material until I was a Junior at the University of California Engineering School! If you have questions emailand I'll try my best to help. Don't let this discourage you since most of the stuff is extremely interesting and explained well. Resources: