https://chrome.google.com/webstore/detail/what-hn-says/claak...
https://chrome.google.com/webstore/detail/hacker-newsd/njdnd...
Also some bookmarklets that you can transform as a Chrome extension with this : http://sandbox.self.li/bookmarklet-to-extension/
http://chetan51.github.com/panels/hacker/
http://see-reaction.appspot.com/index.html