Scott Hanselman has put together a blog posting that provides the source code and application programmer interfaces (APIs) for you to use .NET Framework for you to access information in Web 2.0 sites. His posting is named The Weekly Source Code 22 - C# and VB .NET Libraries to Digg, Flickr, Facebook, YouTube, Twitter, Live Services, Google and other Web 2.0 APIs.
You'll find links to source code and Hanselmann's review of the code and how it works. You'll also see code snippetts so you can check out what the developer is thinking before downloading the kit. In addition to the list in his blog title, you'll find links to source code APIs for WordPress and XML-RPC based blogs and GData.