I'm trying new ways to defend against comment spam, thanks to these sites for providing IP block lists, or links to IP block lists:
http://www.heise.de/ix/nixspam/dnsbl_en/ (this one is more email spam)
Like those pages say, or should say, block lists are not infallible. They probably won't block every bad IP, and they might block some good IPs. Therefore, I'm only using the block list to potentially block those that try to use the HTTP post method. Not only will it result in a lower load on the server, but also prevent legitimate access to my websites.