Hopper

IP-based blocking won’t do a bit of good — at leastr for spam. I watched a spammer post about 150 comments on an MT blog using some 20 or 30 different IP addresses spanning the globe.
It’s not effective, and not worth your time pursuing an IP-based solution. WP-blacklist, along with one or two of the other excellent WP spam blocking plugins, is all you really need.

You can find instructions on how to set up a cron job to automatically grag the latest blacklist periodically. It’s wise to update about every 24 hours. There might be a CGI that will do it as well, but I don’t remember any specifics.