Lifechangers for me were:
Testament of Youth- Vera Brittain, not fiction, so cheating a bit putting it in, but a must-read anyway.
All Quiet on the Western Front- Erich Maria Remarque (should be obligatory reading for all 12 year olds IMO)
Trinity- Leon Uris
(bit more light-hearted, still not fiction, but fab if you grew up in the 70s/80s) Where did it all go right? Andrew Collins
The Little Prince- Antoine de Saint-Exupery
I don't tend to do classics as can't cope with bonnet overload, but I do love Lady Chatterley, Tess and Wuthering Heights. (mind, I'd rather eat my own faeces than battle with Austen)
I loved The Island too, but need to add that The Return is shite. Other Richard/Judy type books that have been good were Lovely Bones, My Sister's Keeper. (be very way of Richard/Judy reads though, very much minefield and either brilliant or totally crap)
Room with a View - EM Forster...."the answer to the everlasting why, is yes and yes and yes!"
The Godfather- Mario Puzo- brilliant, covers the films 1 and 2 (and let's face it, they should never have made the other anyway!)
Great Gatsby/Tender is the Night/The Beautiful and the Damned - Scott Fitzgerald
The Blood of Others- Simone de Beauvoir.
There's a brilliant list in the Guardian (last year sometime, it's still online, 1000 books to read before you die (or something) I am disciplining myself to read 2 airport novels (crime series etc) followed by one huge and heavy tome from the list.