If you’ve been using the beta tools to develop for Windows Phone 7, you’ve had to do without for a little while – but no longer. The RTM tools are available for download! There are a ton of great things included in the package and they have been and will remain completely without cost. So go get ‘em and happy developing! Here are some more great resources to get you going ...
Windows Phone 7 Training Kit for Developers - RTM Refresh Silverlight Windows Phone 7 Toolkit Learn Expression Blend MSDN Docs Microsoft Advertising SDK for Windows Phone 7 Great "Tips and Tricks" post by Tim Heuer Windows Phone 7 Design TemplatesTons of links on WP7
Some good info on using oAuth in a WP7 app. specifically with Twitter:
Building a ‘real’ Windows Phone 7 Twitter App Part 1 Building a ‘real’ Windows Phone 7 Twitter App Part 2 Building a ‘real’ Windows Phone 7 Twitter App Part 3