DD10 would like to learn more about science. She is in a science class but she wanted to learn more. She loves to read and I think it would be fun for her to do some experiments as well. Right now she is interested in learning more about gravity, electrons, planets, galaxy. I'm looking for something more self-contained where she can pull out and read when she wants. Ideas?
Well, I would not recommend RealScience4Kids for that sort of kid. It's very light on the reading. The textbooks are just a few dozen pages long with large fonts text and tons of white space. My 7-year-old read through the Biology I text cover to cover in about an hour and half. These do have an experimental component; while we found these okay, they weren't really the strength of the program. The strength is in distilling out basic principles and presenting them very efficiently in an unintimidating fashion to young children. So I think they're better suited to 7 to 9-year-olds getting their first taste of formal science than to 10 to 12-year-olds wanting more depth and breadth.
Instead you might look at something like the DK Definitive Visual Guide to Science or the DK Encyclopedia of Science. These are full of information and pictures, enough for dozens of hours of reading. And they're inexpensive for what you get. They're missing the experimental component, though, so you'd need to find another source of hands-on stuff. For that I'd recommend "Science Is..." by Susan Bosak.
Mountain mama to three great kids and one great grown-up
If you do use Real Science 4 Kids, go up a level. I agree with pp when said that the level one books are easier than they make out. They are solid, but simple. We used Physics 1 in 4th grade.