One of my Favorite Children’s Authors: Mo Willems
Our first introduction to Mo Willems was his book Time to Pee!
I love this book because it’s very practical and straight forward. It included all the necessary steps and illustrated the feelings a child might have when potty training. The pictures are fun and whimsical. It quickly became our favorite potty training book. Here are some pictures of some of the pages:
He writes a similarly styled book called Time to say Please which I also like. I have to admit to not being as thrilled with his Pigeon series which is his most well known.
We have recently discovered his Elephant and Piggie first reader series which is a collection of silly books where the main Characters are “an optimistic (and sometimes reckless) pig and a cautious, pessimistic elephant.†(copied from Amazon.com Editorial Reviews). 
I really like this easy reader series because Mo Willems is able to provide an amusingly silly story with a small amount of simple vocabulary. Most beginning reader books are very dull in my opinion, so Mo Willem’s collection has been a great find!
Anyway, if you’re looking for a good easy reader, I recommend Mo Willem’s Elephant and Piggie Series.