LOTR, JRR Tolkein- Scarily plausible world, presence of a plurality of themes. Dante probably would've enjoyed it.
The Man Who Was Thursday, GK Chesterton- Your struggle with everything in a nutshell. Probably my favorite book of all time.
Crime and Punishment, Fyodor Dostoevksy- Nihilism, libertarianism, and socialism are given a crack at in a psychothriller long before Hitchcock.
Dune, Frank Herbert- Religion is dead and computers reign in other sci-fi epics...not this one.
Mere Christianity, CS Lewis- If there was no warning about adding to the Bible, I would have tacked this at the end of revelation.
Henry V, Shakespeare- Machiavellian ruler or virtuous English king successfully manipulating the realities of statecraft: you make the call.
Road to Serfdom, FA Hayek- Want to know how republics turn into totalitarian terrestrial Hells? Everyone in government should be forced to read this.
Rules for Radicals, Saul Alinsky- Know thy enemy...
The Federalist, Hamilton, Madison, Jay- Know thyself...
And you shall be victorious