The Picture Book Marathon , created by Jean Reagan and Lora Koehler, is a program dedicated to getting writers to write one picture book a day for a month - allowing for a few rest days in between. I read about this in the Nov/Dec 2009 SCBWI bulletin, and thought it was a great idea! I'm not really a picture-book writer, I've started a few and I have some good ideas ( I think) for others, but I like what Reagan and Koehler have come up with, and I think it's good practice for any writer. I mean, if you think about it, writing a picture book is like writing a really concise, really visual story - 150-800 words max., typically. So that makes for excellent practice for those writers who tend to be "wordy".
If you're interested in joining the picture book marathon, it looks like another one is starting up in February of next year. Visit the website to learn more.
Some of my favorites, below: