The Official Windows Phone 7 Patterns & Practices now available ! You can check them at - http://wp7guide.codeplex.com/
Periodically it will be publishing early versions of deliverable on this site, so keep checking!
At present it has a new guide from patterns & practice which will help you to design and build applications that target the new Windows Phone 7 platform.
Check the site - http://wp7guide.codeplex.com/ for more details and download.