First we recommend you install mod_security on your server, or have your ISP install it for it (its VERY easy to install), then we suggest you install our mod_security rules. We use WordPress for some of our blogs, and as such keep a close eye on vulnerabilities with WordPress and in making sure our rules don't cause problems with normal WordPress use.

Simple, install mod_security and use our Comment Spam Blacklist on our mod_security rules webpage. Its faster than any of the plugins for WordPress, and its more up to date.