'Three Men in a Boat' by Jerome K. Jerome. This is an old - fashioned but still very funny book. Three men decide to go on a boating holiday along the Thames. Their bumbling adventures, misadventures with camping, and their humorous takes on simple things like cooking make it a delightful read.
'The Princess Bride' by William Goldman. It combines elements of fairytale and comedy. With characters like Inigo Montoya on his quest for revenge, and the humorous asides by the author throughout the story, it's a book that has both heart and humor.
'Confessions of a Shopaholic' by Sophie Kinsella. It follows Becky Bloomwood, a shopaholic who gets into all sorts of financial and comical relationship troubles because of her shopping addiction. Her attempts to hide her purchases and pay off her debts in creative (but often unsuccessful) ways are very funny.