Here’s some of ’s own favourite :

  • Opinion Cloud: Summarizes comments on YouTube videos and Flickr photos to provide an overview of the crowd’s overall opinion.
  • Google Voice: All sorts of helpful Voice features directly from the browser. See how many messages you have, initiate calls and texts, or call numbers on a site by clicking on them.
  • AutoPager. Automatically loads the next page of a site. You can just scroll down instead of having to click to the next page.
  • Turn Off the Lights: Fades the page to improve the video-watching experience.
  • Google Dictionary: Double-click any word to see its definition, or click on the icon in the address bar to look up any word.
  • After the Deadline: Checks spelling, style, and grammar on your emails, blog, tweets, etc.
  • Invisible Hand: Does a quick price check and lets you know if the product you are looking at is available at a lower price elsewhere.
  • Secbrowsing: Checks that your plug-ins (e.g. Java, Flash) are up to date.
  • Tineye: Image search utility to find exact matches (including cropped, edited, or re-sized images).
  • Slideshow: Turns photo sites such as Flickr, Picasa, Facebook, and Google Images into slideshows.
  • Google Docs/PDF Viewer: Automatically previews pdfs, powerpoint presentations, and other documents in Google Docs Viewer.
  • Readability: Reformat the page into a single column of text.
  • Chromed Bird: A nice Twitter viewing extension.
  • Feedsquares: Cool way of viewing your feeds via Google Reader.
  • ScribeFire: Full-featured blog editor that lets you easily post to any of your blogs.
  • Note Anywhere: Digital post-it notes that can be pasted and saved on any webpage.
  • Instant Messaging Notifier: IM on multiple clients.
  • Remember the Milk: The popular to-do app.
  • Extension.fm: Turns the web into a music library.

See the rest here:
Use Chrome like a pro