The Gruffalo by Julia Donaldson

I would read this book to my kids every night I was home to do so- it was the first book my daughter ever read to me. My son had memorised it and so it remains a strong link to my kids. While not fancy, expensive or extravagant it is worn and well loved and holds some of my happiest memories within its well-thumbed pages. 

The illustrations are perfect for a child to comprehend and weave into their excitable imaginations and the writing is such that the rhythm and rhyme are simplistic genius.