I’ve included a few links from the Microsoft Platform Ready site to get you started developing your Windows Phone 7 applications. 

Microsoft Platform Ready is a great program to help you get your application to market faster through technical and marketing support. Microsoft Platform Ready is a great stand alone program and/or complement to the MSDN and BizSpark Programs.  To sign up for Microsoft Platform Ready Please visit this link.

MSDN Windows Developer Center

Windows 7 in 7 video tutorial.  Part I and Part II

Getting Started with Windows Phone 7 - Application Development

Start Developing Your App

• Download Windows Phone 7 Developer Tools.  It includes the following:
• Visual Studio 2010 Express for Windows Phone Beta, the Windows Phone Emulator, XNA Game Studio, Expression Blend for Windows Phone, samples, and documentation. (If Visual Studio 2010 Professional or higher is already installed on your development computer, an add-in for Visual Studio 2010 Professional is automatically installed as well.)
• Check out the Code Samples for Windows Phone 7 to review examples of applications built for WP7 and access the Programming Guide for Windows Phone 7 which includes conceptual overviews, how-to topics and code snippets.
• Stay in touch with the latest WP7 developer news here.
• Get registered with the Windows Phone 7 Marketplace.  This will prepare you for uploading your app for testing and then adding your app into the marketplace.  $99 fee for WP7 Marketplace will include 5 application testing submissions.

Other Resources and Information

• Windows Phone 7 in 7 video series can help you get started with developing your WP7 application.
• If you are looking for tools that are available to help you develop applications for Windows Phone 7, it is located at the Application Platform Overview for Windows Phone 7.
• System requirements for setting up the WP7 Developer Tools here.
• Debug your application with the Windows Phone Emulator.
• Review the Execution Model for Windows Phone 7 to learn about how WP7 apps handle activate/deactivate scenarios as other high priority apps take precedent, such as when in incoming call occurs.
• Frame and page navigation guide for WP7 can be found here.
• Information on WP7 APIs can be found here.
• Find instructions on using Silverlight and XNA Frameworks for your WP7 app.  If you are looking to port an existing Silverlight app to WP7 click here.

Support

WP7 Developer Forums

Windows Phone 7 Training Kit

WP7 Developer Blog