This is so hard. I had five planned and then I read the thread.
As my name suggests, I must have Persuasion by Austen. Because when you have a down day, doubting the power of love, or just craving escape you can open chapter 23 and the words "you pierce my soul" make you exclaim out loud and positivity is restored.
Goodnight Mister Tom, again because it restores your faith in humankind and introduces mental illness, grief etc to a young audience in a beautiful way.
So glad Louis de Bernieres was mentioned by at least one person. I saw that they picked the trilogy but if pushed to pick just one I would pick Señor Vivo and the Coco Lord. It shows determination and courage in the face of some of the most awful events and still manages to be funny.
The English German Girl - I am going out on a limb and saying I prefer this to The Book Thief (Holocaust) theme. It is beautiful, devastating and well researched. I read a lot of Holocaust related literature both fiction and non fiction and this is just amazing. Every single person should read this.
Around the World in Eighty Days - fantastic writing, a great yarn and bringing the world to people in 1872. For all of Fogg's flaws I find it an inspiring read to get up and do something.
I could easily add Wuthering Heights (my favourite - but following the rules), Frankenstein and To the Lighthouse (I struggle with Woolf until I just get to a point where she has written a sentence that just turns it all upside down).