Recently a bunch of Web Application Toolkits have become available for download on the MSDN site. The primary purpose of the Web Application Toolkits is to enable Web Developers to simply extend their web application capabilities by providing them with a packaged set of running samples, templates and documentation.
As a result you can find code, documentation and screen casts on the following Web Application Toolkits:
Screen cast details and more on the toolkits is available on this blog post. In my opinion these are some great resources for anyone building web applications, so do check them out!