These are the ones worth keeping an eye out for.

Google sites & blogs

• Chromium OS discuss
  Google Group for discussing all things Chrome OS related.
• Google Chrome Blog
  The latest news from the Google Chrome team.
• Google Chrome YouTube Channel
  Make sure you satch the 'What is Google Chrome OS?' video.
• The Chromium Blog
  Blog of the The Chromium Projects website.
• The Chromium Projects
  Site housing documentation and code related to the Chromium projects: Chromium and Chromium OS
• The Official Google Blog
  Google's most important announcements are posted here.

Unofficial websites

• Chrome OS Site
  Chrome OS Site aims to become the largest online community dedicated to the Google Chrome Operating system.
• Chrome OS-Blog.com
  News and support for Google's open source operating system.
• Google Blogoscoped
  One of the best blogs about all things Google.
• Google Operating System
  An unofficial blog that watches Google's attempts to move your operating system online.
• Wikipedia: Google Chrome OS
  This wikipedia entry gives a good overview of what Google Chrome OS promises to be.

Blogs & Tweets

• ChromiumOS
  Twitter feed dedicated to Chromium OS.