Several years ago I found this great book on cartooning at a yard sale: Ed Emberley's Drawing Book of Faces. Its been handy in so many ways... I've used it as a teaching aid when I volunteer to teach cartooning at my kids' school. I've used it myself as a source of inspiration when designing characters.
But best of all, Simon has spent hours pouring through it and filled pages with characters either taken from the book or created based on the principles Emberley describes.
Here are just a few done on two sides of a single sheet.
I can see why Si glommed onto this book. Emberley's style is immediately appealing and the process he developed
A conversation over at The Retro Kid reminded me of Ed Emberley and one of the contributors over there kindly included this link to Emberley's website.