"Earlier this year I published a series of articles on Codeguru about WP7 Silverlight development. Later on I have remastered them a bit and merged them together with a couple of articles by Vipul Patel into a small eBook that was published on internet.com, called Windows Phone 7 Quick Start Developer Guide. There is also a ZIP archive with the source code for all the sample projects presented throughout the book. While you can still find the articles online on the site, I recommend the eBook as a better learning material as it puts the various topics together.
The eBook is intended for developers with a fair knowledge of .NET programming that want to start developing Silverlight applications for Windows Phone 7. However, it is not a complete guide to Silverlight development for Windows Phone 7. The eBook covers a smaller set of Silverlight topics that is intended to prepare the reader for the most common challenges a Windows Phone 7 developer faces.
Here's a snap from the PDF's table of contents;
I like how the TOC was done... Those pictures add a very nice touch.