You can download Joe Haldeman's classic, The Forever War, for only 1.99$ here.
Here's the blurb:
A THOUSAND YEAR CONFLICT. ONE SOLDIER LIVES THROUGH IT ALL. CAN HE MAINTAIN HIS HUMANITY?
The Forever War is a science fiction classic that chronicles the life of William Mandella. Due to the time distortion associated with deep space travel, he is present during both the first and the last battle of a thousand year old conflict with the alien Taurans.
A masterpiece of not just science fiction, The Forever War illustrates the futility of all wars and their effect on the human soul.
The Forever War won all major science fiction awards including the Hugo, Nebula and Locus. Ridley Scott, director of Blade Runner and Alien, is currently adapting this classic for film.
This is the author's preferred version and includes a foreword by John Scalzi, author of Old Man's War.