PostRank: Ranks popular posts in Google Reader
An extension for Safari and Chrome that ranks and filters items in your Google Reader inbox according to their popularity on various social networks.
It works brilliantly on high traffic feeds with a dodgy signal to noise ration, like Pinboard/del.ico.us tags or sub-Reddits—the kind of stuff you want to skim through, river of news style rather than actively read, item by item.