Add the share-widget button on the footer of your post. Users can share your content through popular social network and email.
A fast plugin for sharing on top social networks, eMail, making HTML links, short links, translations, helping explore your site & Follow you...
Snap Skout's free social sharebar plugin features popular social icons, including Skout. Skout is the easiest way to find the best deals and info
With Share Buttons Widget you can share your content at Facebook, Twitter, Google, Digg, Delicious and many more!
Social Login by Janrain
Google Identity Toolkit (GITkit) helps relying party (RP) websites to support federated login easily (http://code.google.com/apis/identitytoolkit).