Even Firefighters Go To The Potty by Wendy Wax was a big hit with my son. He had reached the point where he knew what he had to do, what we wanted him to do, but simply didn't want to stop doing whatever he was doing to take a potty break. This fun book with lifting flaps showed him that everyone needed to take breaks during the day to use the potty even firefighters, police officers, teachers and baseball payers. Therefore, it would be okay for him to take breaks too.
The Gas We Pass: The Story of Farts by Shinta Cho is a laugh inducing book from the title alone. However the book gives some information along side the chuckles, the whys and hows of gas are explained. Expect laughter and silly noises, but toddlers simply love this book. Everyone Poops by Taro Gomi is another informative but laughter inducing book to share.
There are a large number of potty books out there, and these are some that were received well in my house, your child might rather watch videos or read a different selection of books. I think these are universally helpful and enjoyable by both parents and toddlers.