WPSpamFree is a a powerful anti-spam plugin for WordPress. It eliminates comment spam, including trackback and pingback spam. It works invisibly without CAPTCHA’s, or other inconvenience to site visitors.
The plugin includes a spam-free contact form feature.
Features:
Virtually eliminates automated comment spam from bots. It works like a firewall to ensure that your commenters are in fact, human.
A counter on your dashboard to keep track of all the spam it’s blocking. The numbers will show how effective this plugin is.
No CAPTCHA’s, challenge questions or other inconvenience to site visitors — it works silently in the background.
Includes drop-in spam-free contact form. Easy to use — no configuration necessary.
No false positives, which leads to fewer frustrated readers, and less work for you.
You won’t have to waste valuable time sifting through a spam queue anymore, because there won’t be much there, if anything.
Powerful trackback and pingback spam protection.
Easy to install — truly plug and play. Just upload and activate. (Installation Status on the plugin admin page to let you know if plugin is installed correctly.)
The beauty of this plugin is the methods of blocking spam. It takes a different approach than most and stops spam at the door.
The code has an extremely low bandwidth overhead and won’t slow down your blog (very light database access), unlike some other anti-spam plugins.
Completely compatible with all cache plugins, including WP Cache and WP Super Cache. Not all anti-spam plugins can say that.
Display your blocked spam stats on your blog.
Helps keep your database slimmer and more efficient.
Works in WordPress MU as well. (See the related FAQ for details.)
It’s completely free for both commercial and personal use.
Plugin homepage: http://www.polepositionmarketing.com/library/wp-spamfree/