• “On Liberty” (John Stuart Mill) for political enlightenment and an impeccable defence of [classical!] liberalism. It's packed with simple but enormously powerful ideas that are also timeless, thus applicable today and to so many aspects of life.
• “Don Quixote” (Cervantes): unanimously considered the best work of fiction in the Spanish-speaking world… and on many lists, even #1 of world literature, ever (!). Often overlooked (at least in Spain) by young folks as it is long, the language is archaic, and its themes appear quaint and silly today at first sight. But there's a reason it has been praised for centuries. It's funny and tender. Themes are also modern, and Cervantes' style is playful and innovative, making use of devices such as meta-references, alternative pasts, removal of the fourth wall, etc. I'm not sure how much non-native audiences can enjoy translations, though.
• “The Lord of the Rings” (Tolkien) for the original epic and touching fantasy. (I know many people devour it in their teens, or in their early youth… But I read it as an adult; quite late. Mainly because it seemed to be the only “difficult” book that many of my friends bothered to read, and that predisposed me negatively towards it. Also, my family hadn't read it, and there was no copy of it in our house.)
• “Brief History of Time” (Stephen Hawking): mind-boggling introduction to (astro-)physics, modern cosmogony, etc.
Oh, and don't waste your time with “How to Win Friends and Influence People”; it is definitely overrated! The whole book would fit in a sheet of paper if you took out unscientific anecdotes, redundancy, and obvious instances of common sense...
• “Don Quixote” (Cervantes): unanimously considered the best work of fiction in the Spanish-speaking world… and on many lists, even #1 of world literature, ever (!). Often overlooked (at least in Spain) by young folks as it is long, the language is archaic, and its themes appear quaint and silly today at first sight. But there's a reason it has been praised for centuries. It's funny and tender. Themes are also modern, and Cervantes' style is playful and innovative, making use of devices such as meta-references, alternative pasts, removal of the fourth wall, etc. I'm not sure how much non-native audiences can enjoy translations, though.
• “The Lord of the Rings” (Tolkien) for the original epic and touching fantasy. (I know many people devour it in their teens, or in their early youth… But I read it as an adult; quite late. Mainly because it seemed to be the only “difficult” book that many of my friends bothered to read, and that predisposed me negatively towards it. Also, my family hadn't read it, and there was no copy of it in our house.)
• “Brief History of Time” (Stephen Hawking): mind-boggling introduction to (astro-)physics, modern cosmogony, etc.