Cheerios (the cereal, not the Glee cheerleaders) will be putting children's books in boxes of O's in 2010. You can help choose the titles. I've heard you can vote through October 30th, and maybe more than once. Maybe even more than once a day.
But since I got that info through a listserv, it's kind of like gossip. Nonetheless, there's no doubt that you can vote because the buttons are right there.