MonoCross - The Technology
Some very interesting thoughts on cross platform development, along with an open-sourced framework that practically implements it.
The Mono team has since been retrenched, but keep an eye on Xamarin (from those very same developers) for some exciting developments in the cross-platform space.
Creating WP7 promotional videos
Portable Library Tools
Single library - multiple .NET platforms
Top 8 Websites To Learn Windows Phone 7 Development
WP7 Launchers - Mango (Windows Phone 7.1)
Resources for Windows Phone Mango Developers
PinCodeKeeper WP7 app - Submitting to Marketplace
Building a detailed About page for your Windows Phone application
Silverlight Touch Library
Provides some parity with the touch API found in the windows phone silverlight framework
18 hours ago