A bunch of books for children with very colorful illustrations of the main character, usually a monster. They were written by Stephen Cosgrove and illustrated by Robin James.
The books always have a progressive theme to them, such as cleaning up your room, or caring for the environment. My favorites are Bangalee and Creole.
Web link of note: Listmania: Serendipity Books
(At http://www.amazon.com/exec/obidos/tg/listmania/list-browse/-/3ENJHE93NFZTX/ghosthouse01-20)