Lip service is paid to the saying "the best things in life are free." It happens to be true, especially with literature; a great deal of the best things ever written are in the public domain.
Here's some classics that I can personally vouch for being worth reading over and over:
Pride and Prejudice
Walden
Thus Spoke Zarathustra
Siddhartha
Romeo and Juliet
Hamlet
King Lear
MacBeth
Leaves of Grass
