Well I've just come from The Art of Manliness and their reading list, so I was inspired to put together my own. I haven't tried to rank them. This list is more of books that people actually read, not just say they've read.
Starship Troopers by Robert Heinlein - pro- military
The Forever War by Joe Haldeman - anti-military
Old Man's War by John Scalzi - third view of war
With Fire and Sword by Henyrk Sienkiewicz - 19th century adventure novel
1984 by George Orwell - brutal dictatorship
Brave New World by Aldous Huxley - dictatorship of comfort and free sex
Catch-22 - by Joseph Heller -anti-military and founded a new phrase
The Curse of Chalion - Lois McMaster Bujold - what it really means to do God's will
Dune by Frank Herbert - Messiah in space
Double Star by Robert Heinlein - doing your duty although it erases you.
War and Peace by Leo Tolstoy - human nature, and some comments on war
A Princess of Mars - by Edgar Rice Burroughs - honor, courage, rip-roaring adventure.
Tuf Voyaging - George R R Martin - for some reason, Haviland Tuf appeals to me.
Callahan's Cross Time Saloon - by Spider Robinson. Shared pain decreases.
Day of the Triffids by John Wynham - end of the world via biological warfare.
Huckleberry Finn - by Mark Twain
The Hobbit - J RR Tolkien - of course
Lord of the Rings - J R R Tolkien - natch.
Macbeth - Shakespeare - murder, treason, guilt!
Ender's Game - Orson Scott Card - kids are smarter than adults
A Wrinkle in Time - Madeleine L'Enge
Dracula - Bram Stoker
Startide Rising - David Brin
Have Space Suit - Will Travel by Robert Heinlein
Hyperion by Dan Simmons - kind of have to read the sequel Fall of Hyperion also
Watership Down - Robert Adams