Luigi Cavalieri

RedBrick is able to block most of the automated spam comments a WordPress blog receives daily.
It is based upon a score system that ensures spam comments are blocked as soon as possible, so as to minimise the number of checks each comment must go through. When in doubt, RedBrick always holds the comment in the moderation queue. Comments identified as spam, however, never reach the database.
As a last resource in discerning the kind of comment under examination, RedBrick takes account also of the comment author’s history.
The plugin is designed to work on low-to-medium traffic blogs.

RedBrick

Simple anti-spam plugin for WordPress blogs.

blackmelvyn

tiger

This plugin has been developed by BlackMelvyn from this <a href="http://www.theblackmelvyn.com/" title="SEO Black Hat blog" rel="nofollow ugc">blog SEO Black Hat</a> thanks to a script coded by Tiger from <a href="http://www.seoblackout.com/" title="Référencement Google" rel="nofollow ugc">Blog SEO BlackOut: Techniques référencement Google</a>. 
It compares the language contained in the comment text to the languages that you allow in your admin panel for this blog. 
There is a minimum confidence index that should be reached for the comment to be considered as valid. 
Then, if the comment is sorted a valid, it is held for moderation. 
On the other hand, the plugin counts the number of links contained in the comment, and if there is a suspicion of comment spam, it blocks the comment and adds it to trash. 
Finally, you get rid of all these automated spam bots that try and spoil your blog with their nasty unuseful comments, you save database space and you save time as you do not have to sort out what is spam and what is not! 
We recommend that you use this plugin in conjunction with the keywords filter built in WordPress for more efficiency.

Language-based Comment Spam Condom

This plugin prevents comments spamming using language verification.

RedBrick vs Language-based Comment Spam Condom