YouTube blog shared useful Chrome extensions for YouTube, here they are.
Windows Expander for YouTube fills entire browser window. This extension is useful for multiple monitor setups.
Turns off the Lights turns the entire page from fading to dark which makes you feel you’re watching movies from theaters.
Opinioncloud summarizes comments on YouTube videos and Flickr photos to provide an overview about the crowd’s overall opinion.
YouTube Feed from Google notifies whenever new videos are available in your YouTube homepage feed. You can directly access videos that your friends upload, rate and like right in your browser. This extension is useful if you have friends or subscriptions in YouTube as you can receive instant notification whenever new content is available.
Via [YouTube blog]