Pretty much my favorite book when I was a kid: [youtube=http://www.youtube.com/watch?v=fWIdkYk9fQM]
According to Wikipedia:
The original concept for the book featured horses instead of monsters. Sendak said he switched when he discovered that he could not draw horses.
The Wild Things (except "Goat Boy", of course) were named after (and are presumably caricatures of) Maurice's aunts and uncles.