I just got the newest Old Schoolhouse Module -- Let's Be Scientists and it looks great. Rather than focusing on one specific branch of science, this gives you a great overveiw. There are sections on weather, astronomy, chemistry, and anatomy.
Let's Be Scientists also has great experiments like "Ice Cream in a Bag" and "How Do Your Taste Buds Work". There is also an introduction to gross science which most kids will love.
As always, there are great quizzes, copywork and coloring pages. There are also recipes included that I can't wait to try.
Check out Let's Be Scientists.