FolioVision

There’s one problem with Gravatars. They are very slow to load. Each page with comments on them makes one call per comment to the Gravatar server. While a single call takes only a 100ms, on a page with hundreds of comments, we are talking about major slowdowns. Page loads can take 20 seconds and more.
This plugin solves this problem by:
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<li>
caching gravatars with WordPress cron job..
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<li>
caching gravatars on comment submission
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<li>
maintaining a single copy of the default gravatar instead of downloading it again and again for all the email addresses with no gravatar associtated
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</ul>
<a href="http://foliovision.com/seo-tools/wordpress/plugins/fv-gravatar-cache/installation" rel="nofollow ugc">Installation guide</a>
<a href="http://foliovision.com/seo-tools/wordpress/plugins/fv-gravatar-cache" rel="nofollow ugc">Support and more information</a>

FV Gravatar Cache

I deactivated plugin but still contains elements in Database

Database Junk

Speeds up your website by making sure the gravatars are stored on your website and not loading from the gravatar server.

Dougal Campbell

This plugin allows you to automatically add Gravatars for commenters to your 
theme, if your theme does not already support them.
According to the Gravatar.com website, Gravatars are Globally Recognized 
Avatars, or an “avatar image that follows you from weblog to weblog 
appearing beside your name when you comment on gravatar enabled sites.” 
You register with the Gravatar server, and upload an image which you will 
use as your avatar. The gravatar image is keyed to your email address, so 
that it is unique to you.
This plugin will display gravatars for the people who comment on your posts. 
You do not need to modify any of your template files — just activate the 
plugin, and it will add gravatars to your comments template automatically.
<h3>Credits</h3>
Based on a code snippet from Matt Mullenweg: 
 http://photomatt.net/2007/10/20/gravatar-enabled/ 
 http://pastebin.ca/743979
Props to David Potter for pointing out that Gravatar normalizes email 
addresses to lowercase before hashing with MD5: 
 http://dpotter.net/Technical/index.php/2007/10/22/integrating-gravatar-support/

Easy Gravatars

nice

Add Gravatars to your comments without modifying any template files. Just activate, and you're done!

FV Gravatar Cache vs Easy Gravatars