One of our main science focuses this school year has been with the study of rocks and minerals.  We are rockhounds anyway, so the research material we used was readily available.  We probably own at least 10 various books on the subject, and also have a rather large collection of fossils and other rock and mineral specimans. 

A few times a week, we'd read from one of the books, do some worksheets I'd either design or find on the internet and right any new words in their "Word Books" along with the definitions.  We often examined our collection to find examples that fit with whatever we'd read about.  We purchased several unique specimans from ebay and the kids had great time showing them off and telling all about them.  We would also look around us as we'd be in the yard or while driving.  They'd notice different rock formations, layers of rock base in mountain cut-outs along the highways, boulders excavated while strip-mining, unique specimans while walking, among other things.