Pippin Williamson

Modifies the Empty Spam action in WordPress to process the spam deletion in batches, allowing you to delete thousands or even hundreds of thousands of spam comments at once without killing your server.
Have you found a bug or have a suggestion or improvement you’d like to submit? This plugin is available on <a href="https://github.com/pippinsplugins/batch-comment-spam-deletion" rel="nofollow ugc">Github</a> and pull requests are welcome!

Batch Comment Spam Deletion

Modifies the Empty Spam action in WordPress to process the spam deletion in batches instead of all at once.

skunkbad

<a href="http://blog.skunkbad.com/wordpress/the-comment-redlist-plugin" rel="nofollow ugc">Comment Redlist</a> is a WordPress plugin that blocks comment spam before it is inserted into your database.
Manage your Comment Redlist settings on the Settings > Discussion page, or on the plugin’s dedicated options page, located in the Settings menu.
For more information, check out <a href="http://blog.skunkbad.com/wordpress/the-comment-redlist-plugin" rel="nofollow ugc">http://blog.skunkbad.com/wordpress/the-comment-redlist-plugin</a>.
Features include:
<ul>
<li>Comments blocked by word, character sequence, or IP address.</li>
<li>Blocked comments can be logged for debugging or your general information.</li>
<li>Optional javascript alert informs site visitor if Comment Redlist will detect their submission as spam.</li>
<li>Optional setting provides spammer with zero feedback, instead of an error message.</li>
<li>Optional form tokens use cookies (PHP session) to confirm a legitimate post.</li>
<li>Optional setting restricts comments to US keyboard characters, or any regular expression.</li>
<li>Optional setting removes your comment form’s Website field, and blocks any comment that contains one.</li>
</ul>

Comment Redlist

Easily block obvious spam before it is inserted into your database.

Batch Comment Spam Deletion vs Comment Redlist