Bannage allows you to do just what the name implies: Ban.
Introducing, Bannage, a plugin for WordPress that allows the administrator of a wordpress powered site to ban comments via usernames, email address, ip address or URI. If you have fallen victim to spam comment entries and such plugins as Akismet are not getting 100% of it. You can attempt to prevent spam using Bannage!
Ban comments by:
3. Email Address
4. IP Address
Allows multiple entries for each ban type.
A great idea, as I can think of some IP Adresses I would like to ban. Though no doubt I have to be careful, as those spammers are crafty people. Check it out at Justin Shattuck’s blog.