After a few google search I found these:

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