Bookends are the kind of item you will probably never need to buy—but that doesn't mean you won't. Of course, they're not really necessary on a bookshelf if you have enough books to fill the space, and if you are placing books on an open table or desk, you can always use vases, paperweights, pencil cups, or picture frames for balance.
But if your books are just too heavy to stand up on their own, try this incredibly simple bookend project from Evil Mad Scientist Laboratories. The team here keeps a stack of textbooks contained between two sleek white bookends—which, if you look closely, are just bricks covered in white paper. They're dressed up with printed physics symbols; the site says that these are bra-ket notations, used in quantum mechanics, but there are plenty of other symbols you could use: b and /b if you're an HTML fan with a bold book collection; the alpha and omega letters to remind you of your fraternity days; your initials, favorite photos, or the first and last sentence of one of your most adored novels.
Bricks usually cost much less than $1 at your local home improvement store, but you (or your neighbors) likely have some hanging around in the garage anyway. The paper wrapping isn't strictly necessary, but it will keep your shelves cleaner and let you add your own touch to the finished product. (Via Make)