Definately Up the Duff but i'd recommend getting another one as well - one with week by week pictures etc, Up the Duff is very funny but sometimes didn't have as much info as I wanted.

Also when you're looking try and make sure the books have been writted in the last 5 years or so. I was given heaps of books written in the 70's and 80's and although they had been updated the pictures were hillarious! The men all had long hair and facial hair and the chapters on maternity clothes were classic! "Every woman should have at least one pair of dungarees and one all in one jump suit!!!"