This book’s so new that I’m not sure the dead-tree version is available yet: it’s Windows Phone 7 Game Development, published by Apress and written by Adam Dawes. I’ve just purchased the ebook version (which you can download right away for USD$34.99), so I’ve only had a chance to do a quick skim.
According to Apress’ site, here’s what you’ll learn from Windows Phone 7 Game Development:
It looks like a worthy partner to Beginning Windows Phone 7 Development.
This article also appears in Global Nerdy.