w3prodigy

Returns ‘Page Not Found’ 404 error message for IP’s visiting your blog specified in the IP Ban option on the Discussion Options page.

IP Ban

Returns 'Page Not Found' 404 error message for IP's visiting your blog specified in the IP Ban option on the Discussion Options page.

Skyy

This plugin allows you to banned certain username from making comment, particularly when you don’t want to ban 
ip addresses, but want to stop certain “notorious” misbehaving users.
If your blog requires user registration, you should really try the “members.0.1.1” wordpress plugin.

IP Ban vs WP-Ban-User