Question: How many of this year's Caldecotts (there are four, the medal winner and three honor books) feature decorated endpapers?"
Answer: Two. [The others have plain endpapers: A House in the Night's are marigold to match the illustrations; How I Learned Geography's are...brown, like a manila envelope.]
A Couple of Boys Have the Best Week Ever by Marla Frazee (Harcourt, 2008). Susan has convinced me that A Couple of Boys Have the Best Week Ever could have (and possibly should have) won the Caldecott Medal outright. Its endpapers feature photographs (the old-fashioned kind, with deckled edges on opposite sides) of the boys' activities at Nature Camp. We never actually see them at Nature Camp in the book--just in the car on the way there and back--so the endpapers are a bonus. They're different in the front and back (these are the front endpapers; the jacket is pasted down, sorry).
A River of Words: The Story of William Carlos Williams by Jen Bryant; illustrated by Melissa Sweet (Eerdmans, 2008). These endpapers are a leafy green with some colored pencil and collage elements. Five of Williams's poems appear on the front endpapers (shown here) and four more on the back endpapers, nicely arranged so as not to be obscured by the jacket flaps (ahem).
But wait! Those aren't the only endpapers here. Many of Melissa Sweet's illustrations for A River of Words were painted or collaged onto the endpapers of old library books. She writes in an illustrator's note:
"[Then] I looked to a big box of discarded books I had from a library sale. One of the books had beautiful endpapers and I did a small painting on it. Then I took a book cover, ripped it off, and painted more. The book covers became my canvas, and any ephemera I had been saving for one day became fodder for the collages."
My favorite of these is the image of Williams stretched out beside the Passaic River (Gurgle, gurgle--swish, swish, swoosh!). Sweet incorporates the vining floral pattern of the endpapers into her painting; it's the meadow grass Willie is lying on.
I think that more than makes up for the other two.