He is most well known for "Where The Wild Things Are" (which I paid tribute to in Nubbin form a couple years ago). Somehow, I never had a copy of "Where the Wild Things Are" while growing up, but I had another book he wrote "Chicken Soup With Rice"...(which I just happened to read to my friend's kids the other day while babysitting)
The book I had when I was a kid came with a 45 record with a song where the lyrics were the words of the book. When reading the book, I still hear the song in my head, even though I haven't heard he song for years and have no idea where the record is (it's probably at my parent's house somewhere).
It is a sad thing that there is one less writer in the world...but he left behind some of the most beloved children's books of our time.