Starship Troopers by Heinlein was immensely influential to me; I first read it at 9 years old, read it at least once a year after that. It was a major influence in my joining the Marine Corps, and I was surprised to find several other Marines who echoed that sentiment--it's also one of only two science fiction books on the USMC's Professional Reading list, the other book being
Ender's Game by Orson Scott Card--another good read itself.
Guns, Germs and Steel by Diamond is very good, as is
Carnage and Culture by Victor Davis Hanson.
The Hobbit was read to me as a bedtime story by my Dad every night when I was 4, I finished off T.H. White's
Once and Future King when I was about 10. The LOTR Trilogy goes without saying, though I found later in life that you really need to read
The Silmarillion to fully understand it.
I suppose there are others but it's late into a midnight shift and I'm writing off the cuff.
Oh yeah, Robert E. Jordan's series is good, if only he'd write faster!!!
Last books read were a couple on George Washington:
1776, and
Washington's Crossing, which got me on a binge of Revolutionary War wargames.