Mine was Where the Wild Things Are written and illustrated by Maurice Sendak.
Actually, this forum can be a bit like that book sometimes; a wild rumpus.
Maybe that's why I'm here so much...
I also really liked The Very Hungry Caterpillar by Eric Carle, because it was the only book that actually encouraged you to stick your fingers through the pages.
And of course, all the Dr Seuss books, but Green Eggs and Ham was the best imho.