The WP Spam Blacklister is a simple spam-prevention plugin that adds the IP address of a marked spam post on WordPress' comments blacklist.
Geo-Captcha shows a captcha image only to countries you don't trust. Geo-Blacklists allows you to disable comments for some countries.
Grants or denies access to a list of IP addresses
SiteBrains blocks spam posts using a completely configurable set of rules. Both interactively as the user types and on our servers upon submission.
Check if a visitor is listed on httpBL.abuse.ch, see http://dnsbl.abuse.ch/faq.php#about_httpbl for more information.
Adds Whitelist and Blacklist options for Trackbacks and Pingbacks
NoFollow Free removes the "nofollow" tag from your WordPress blog's comments with a lot of custom options and provides the option to insert a "NoFollo
Bans IP addresses that have been caught and blacklisted by Spam Karma more than 5 times.
Provides the ability to retrieve information on a commentators IP address without leaving the "edit-comments.php" page.
Provides a simple means to integrate tools provided by Project Honeypot to capture spammers and link harvesters that visit your blog.