Here is a collection of Magento Extentions for social networking.
Facebook Discount Extension
Improved Social Media Presentation
Modern customers like to share their favorite products with their social circles.
Magento Cateyes Seo
Social Feed – Sliding Tabs Media
Advanced Social Life Stream – Magento Extension
Social Life Stream makes it easy to pop your online activity everywhere in your magento website.
Magento Social Login
DH Social Login
The DH Social Login is module helps the user to login with their existing social networking sites like facebook, twitter, google and yahoo.
Product Review Comments
This module allow customer to put their comment on product review.