The first book I ever did was for Fathers Day. My oldest was learning his alphabet at that time, so I thought it appropriate to do "The ABC's of Daddy". I took a picture of the boys holding the alphabet chart together (baby in the bumbo seat, which of course, was on the ground). I did A is for...and found pictures of things we already had for inspiration: Aquarium (a neat pic of daddy and son watching a shark, their reflections in the glass), trips Abroad (a pic of us all outside Buckingham Palace), love that is Absolute (a picture of us on a date), and Admire (daddy staring eye to eye with our youngest as a newborn). I was able to find something for all the letters, although I was kinda stretching it for Q and had to look in the dictionary for inspiration for X. :) That book actually made Jeremy have a little choke and tear!
We've also done "I want to be a cowboy" when he was going through a big cowboy phase and we had lots of pictures of him dressed as a cowboy, doing pony rides, riding the mechanical bull, feeding horses at a charity thing, watching a rodeo, pictures from the stockyards where they held some classes by a covered wagon and did herded cattle down the street, etc. We've done "Summer Days" one, and a "Who loves baby" book which is actually a family tree book....pictures of him with different family members so we can look at it and he can know they love him, even though we live far away and can't see them often.