Many of the most famous works in Italian go back to Medieval and Renaissance times. Generally, works from this time period are harder to read than modern Italian. The most well known works of this time were by: 

Dante Aligieri - 1265 - 1321, know for The Divine Comedy (1320

Francisco Petrarch - 1304 - 1374, Italian poet - considered by many to be the 
Father of the Italian Renaissance

Giovanni Boccaccio 1313 - 1375, Italian pet and scholar, best known for the Decameron (1351)

Other works from this time period incude:

Luigi Pulci (1432 - 1484) known for Morgante, a peom about a giant who is converted to Christianity

Matteo Maria Boiardo (1440 - 1494) an Italian poet known for the epic poem Orlango innamorato

Reading librettos of operas is much like reading a play. A libretto is the script of an opera. I enjoy reading them because I enjoy reading plays in English as well as in other languages.  A web site that has information and librettos in Italian and English can be found at http://www.murashev.com/opera/Operas

For those of you who are interested in classical music, I have included a page on operas, since many of them are written in other languages, especially Italian.  On this page I will list some of the major operas and information concerning the composers and the language and year in which they are written.Berlioz, Hector (1803 - 1869), French composer, Les Ttroyens (opera in French) (The Trojans) (1858)

Monteverdi, Claudio (1567 - 1643), Italian composer and priest, L'Orfeo (opera in Italian), (1607)

Verdi, Giuseppe (1813 - 1901), Italian composer, Aida (opera in Italian), (1871)