(This book is absolutely ace, I just loved it every single bit of it, finished it in record time and I'm a notoriously slow reader)
War and Peace - Leo Tolstoy
(I'm still working on this beast, it's been almost a year now, but when I've had a chance to read it between studying, exams and other books it's always been darn good)
1984 - George Orwell
(gee, who doesn't have this on their list?)
A Sand County Almanac and Sketches Here and There - Aldo Leopold
(an early work on conservation, some of the language seems a bit old fashioned anthropomorphising the animals a little but this man new his environment. In particular read his essay on Land Ethics, it ought to be compulsory reading for everyone)
On the Road - Jack Kerouac
(The Beatnik bible, before they became too concerned with infighting, coffee and bad poetry they went on mad road trips across the US and into Mexico, living life as fast and as full as possible, experiencing everything they could)
Into the Wild - John Krakauer
(The true story of Chris McCandless, who chose a different way through life, essentially chose a life as a bum but lived more in his few years than many people ever do. Essentially a modern day Thoreau. Tragically lost his life after living off the land in Alaska for 113 days by eating a plant that at that point hadn't been known to be poisonous. You'll both love him and hate him, but despite it all the guy's a personal hero to me)