Three Men in a Boat by Jerome K Jerome is quite a humorous book. I remember having an extract of it in school. The book is about the boat trip that a person called J (I believe the author himself) takes along with two of his friends George and Harris.
I feel that the humour is the dry British sense of humour that we all read about.
The second book in this series, is Three Men in a Bummel, about the cycling trip that J, George and Harris take to Germany. Again humorous and readable.
A must read