can't pin point one – think it depends on when and at what age
from my childhood
wind in the willows – kenneth grahame
teens to young adult
anything by George Orwell – I also read quite a lot of political stuff, which won't be a surprise to people who know me.
I'm also a big fan of Kerouac. First book my wife bought me was On the Road – read it from cover to cover in one sitting (I was on the dole at the time).
Cormac McCarthy tells a good tale, my favourites in no particular order, Outer Dark, Child of God, Blood Meridian.
Book I really enjoyed a few years ago was 'Stone Junction'by Jim Dodge. I've also just read (i.e. yesterday ) Fup by him which is quite funny.