I created a simple plugin which, when activated, refuses any comment that contains a spam word listed in Options>Discussion>Comment Moderation
This method checks the comment body, author, email, url, and poster's IP address against the Comment "common spam words" listed. Because it also checks IP, it can effectively blacklist an IP from posting comments, simply by adding the IP to the "common spam words".
This plugin is currently available at: http://www.stationlabs.com/index.php?page=spamwordblock
I apologize if something like this has already been written... I tried several other spam blockers, but nothing was very simple for others to setup, though I'm certain they're very effective as well.