One of my all-time favorite homeschool tools are these paperback book covers. They are library-quality, and while a little pricey, definitely save the cost of buying the book again and again. Once covered with these stiff plastic covers, a paperback book is a durable as a hardcover book, so it can be passed on to student after student.
I cover all non-consumable paperbacks, and even if the book is already a little dog-eared, these covers will make them last. They are easy to do -- each one takes less than five minutes.
Prices are for ten covers of each size.