I've read Lord of the Rings a couple of times, first as a youngster and then when I heard they were making the film I re-read it in preparation. Better second time around.
Other than that I like to read:
'In Dubious Battle' by John Steinbeck at least once a year. I love the American writers of that generation but John's humanity puts him head and shoulders above the rest, at least for me.
'Nausea' by JP Sartre, have to re-read it everyone once in a while, always get something different from it.
I was also stuck on holiday once with only one book: "Bill the Galactic Hero" by Harry Harrison which I read twice by default.