All the Murakami books because there is always a hilarious part in each one that works for one of your more cynical days. The ones i could re-read forever are:
After Dark
Wild sheep chase
Dance, dance, dance
Hard-Boiled Wonderland and the End of the World
the Elephant Vanishes
Kafka on the shore
South of the border, west of the sun
All the classic literature books like:
Shakespeare's works 'cause their all somewhat amusing in their own way.