This has become a bit of a problem on our forum as well.
I started off banning IPs and subnets with .htaccess but since it's impossible to stay ahead of the curve, came here looking for a solution. That list of IPs is great! I've added them to the collection but I also found an add-on here called
Akismet Anti-Spam which I've now installed and will see how that works out for us.