Pat Hawks

When Gravatar has no image on file for a user, this plugin takes over and searches for a Facebook, Twitter, or Gmail profile picture to use in it’s place.

Better Avatars

Replace empty Gravatars with profile images from Facebook, Twitter, or Gmail

anantgarg

The Third Party Accounts Login plugin allows you to enable your users to comment via well known OpenID service providers like Google, Yahoo, Flickr etc. The functionality is similar to that provided by StackOverflow and RPXNow.
The plugin allows the user to provide his/her details via all the famous OpenID service providers (Google, Yahoo etc.) while commenting. A working example of the plugin can be found on http://anantgarg.com
To make this plugin work make sure you have OpenID for WordPress Plugin installed.

Third Party Accounts Login

Enable your users to comment by entering their name/email/website details via well known OpenID service providers like Google, Yahoo, Flickr etc.

Better Avatars vs Third Party Accounts Login