If you're investing over the long haul and have a bit of money to spend, rare books and other literary treasures could prove highly profitable. In 2002, the National Library of Ireland acquired a trove of papers from author James Joyce for $11.7 million [source: Lavery]. Even contemporary authors can command a huge price.
The key is to buy books that interest you and to buy them in the best possible condition. Don't expect to find too many rare books in your local antique store or at the neighborhood garage sale, however. Book dealers and auctions are the best source of acquiring rare books. Moreover, a book that is popular is a better investment than an older unpopular book [source: The Independent]. Signed books are also in demand, as are first editions. Some book dealers make money by investing in new authors, betting the value of these works will increase over time [source: The Independent].