In our modern, multi-media world, the idea of a "bookcase" is almost quaint. The items many people use as bookcases are sold as "entertainment storage units" and can also be used for CDs, DVDs and other media. These often come with adjustable shelves (to accommodate the variance in height between CDs and books) and are sold unassembled at places like Wal-Mart and Target.
These pre-fab storage units usually function well enough as bookcases, CDs racks or knickknack holders, but they lack the elegance and stateliness of the old-fashioned bookcases. They are usually made of cheaper material, too, and are not nearly as sturdy. They work well if you only have a couple dozen books to display, which is common today, as many consumers own far more CDs and DVDs than books anyway.
If you have a large library of books, a more traditional bookcase may be in order. The price range on these bookcases run the gamut, all the way from hand-crafted mahogany cases to less costly but still elegant shelves available at places like Pier 1 or Pottery Barn. The difference between them and the "entertainment storage units" is that these bookcases are usually made of higher quality wood and have the look of a traditional bookcase. The more expensive ones come already assembled and finished, but you can get very nice-looking some-assembly-required bookcases for a reasonable price.
Another option is having shelves built directly into the walls of your home. This is almost always done when the home is being built, though it is possible to add them after the fact. Built-in shelves save space, obviously, and are sturdier than even the strongest freestanding bookcases. (There's no way to knock over built-in shelves unless you knocked the whole house over!) They are especially prized in small apartments or homes where space is otherwise at a premium. It's an option worth considering when looking for a new home.
