Hearing that, I've elected to do the same. Nearly every Saturday, I visit one of our branch libraries and choose from among new and classic picture books to review. Yesterday, I chose several new books including Extra Yarn by Mac Barnett, The Monster Returns by Perter McCarty, and Red Sled by Lita Judge. All great stories with varied illustration styles. I noticed each story had at its core a theme of helping others. Classic. I hope to incorporate that to a greater degree in the picture book story I'm working on now.
Want to look for more underlying themes? Check out this list of favorite books compiled in 1999 and then updated in 2007 by TeachersFirst. Find your favorites and see if they appeal due to an underlying and connecting theme.