Introducing ‘WP-BlockYou’, a plugin by this* (ThisWebHost).
WP-BlockYou, simplified, is a plugin that will block people (via IP address) from visiting your blog and then redirect them to a URL of your choice. It works by adding lines to your .htaccess file, and does not hook into WordPress at all, except for graphical management.
The plugin was written by myself (Jules) to resolve an issue a client was having with comments on their blog. Someone was leaving highly negative comments, and despite blocking the user from posting further comments, they didn’t actually want the user to be able to browse their further articles, and thus leave negative comments elsewhere. Initially I simply added the lines to .htaccess files myself, but thought there must be a tidier and better way for clients to be able to do the same. And so here it is
Be sure to read the README file included