He was best known for the hugely popular "Where the Wild Things Are", originally published in 1963 and still flies off shelves in bookstores to this day. He also co-created the 70's hit stage show and TV special "Really Rosie" with Carole King. I had the soundtrack on LP of Really Rosie and listened to it over and over again when I was a kid. Some seminal memories he's responsible for.
Here's a funny clip from an interview he did about the technology of the future (some language)
Maurice Sendak on Ebooks (http://www.youtube.com/watch?v=0mPEZj21NmE#ws)
This is sad. I read "Wild things' soooo many times to my kids.