"We all float down here. Resistance is futile."
But to the point (Batman)! Bearing in mind I'll read 99% of books at least 2-3 times, here are some I return to more often that others:
The Murder of Roger Ackroyd - Agatha Christie
The Adventures of Sherlock Holmes - Sir Arthur Conan Doyle (part of a complete collection I keep trying to get through in one go)
Do Androids Dream of Electric Sheep? and A Scanner Darkly - Philip K Dick
Fatherland - Robert Harris
The Hannibal Lecter Omnibus - Thomas Harris (though I usually call it 'The Hannibal Lecter Om-nom-nom-nibus'. Because I'm like that.)
The Rats, The Survivor, The Jonah, Shrine, Sepulchre, Haunted - James Herbert
Night Shift, Skeleton Crew, The Stand, The Bachman Books, Pet Sematary, Bag of Bones, Hearts in Atlantis, From a Buick 8 - Stephen King
Strangers, Watchers, Dark Rivers of the Heart, Strange Highways, Intensity, Fear Nothing, Seize the Night, False Memory - Dean Koontz
1984 - George Orwell
The War of the World, The Time Machine, Tono-Bungay - H. G. Wells
The Day of the Triffids, The Chrysalids - John Wyndham.