SharePoint SDK and Whitepapers. Check out some of the new things that they have released!
This upgrade includes more than 200 new topics, including:
  • SQL Full-text Search Syntax
  • Protocol Handlers Reference and Overview
  • An expanded introduction to SharePoint Portal Server Expanded Concepts and Architecture section with new topics about
  • Profiles and Personalization
  • Search
  • Enterprise Application Integration

Also published recently on MSDN: