What are some books with the theme of hope? - I have chosen books like The Great Gatsby and A Thousand Splendid Suns. However, I need another title that has the theme of hope in it. - I am interested in something during World War II, and another with interesting ideas about hope!

Two very good books about hope that use World War II for their settings would be Laura Hillenbrand's Unbroken: A World War II Story of Survival, Resilience, and Redemption and The Diary of Anne Frank.
Hillenbrand's work focuses on the life of Louis Zamperini. He served in the air corps in World War II and was taken prisoner by the Japanese.  While imprisoned, he suffered some of the worst physical and mental forms of torture. He did not submit to the abuses, and remained "unbroken."  
Once Louis returns from World War II, civilian life is a struggle. The intensity of processing the horrific reality left a mark on Louis.  His story is a very powerful account of what William Faulkner would say is the human capacity to "suffer, endure, and eventually triumph." Louis comes to the realization that "divine love" saved him, and allows him to overcome anger's bitterness.  The story's theme of hope is evident in Louis's journey to emotional restoration.
The Diary of Anne Frank focuses on hope during the Holocaust.  The diary is a collection of thoughts from thirteen-year-old Anne Frank.  She and her family were forced to hide as the Nazis took over the Netherlands. Anne receives a diary as a birthday present and keeps it as a log of her time in hiding.  
Anne's voice matures over the course of the diary.  It balances the hope and despair intrinsic to the Holocaust. Anne's voice reminds us that while disgusting acts and actors can permeate our world, they will never be successful in eliminating the restorative hope in it.  This dynamic is seen in the diary's final entry:

...because when everybody starts hovering over me, I get cross, then sad, and finally end up turning my heart inside out, the bad part on the outside and the good part on the inside, and keep trying to find a way to become what I'd like to be and what I could be if ... if only there were no other people in the world.

In the midst of the Holocaust, Anne is hopeful.  She is "trying to find a way to become what [she'd] like to be and what [she] could be."  This standard of hope is something to which all of us should aspire.