Comment blacklisting works well, but what if you actually want to stop someone from even reading your blog? This plugin will take care of that for you.
It uses .htaccess file modifications to deny access to your blog from particular IP addresses (Deny from) and then follows up with an ErrorDocument 403 redirect to a URL of your choice. It doesn’t hook into WordPress, which makes it a lot faster due to no database or PHP calls.

WP-BlockYou

A plugin that can be used to block or "ban" users via their IP address from viewing your blog, and then redirecting them to a URL of your ch …

MarkTroll is a simple WordPress plugin that implements user <a href="http://en.wikipedia.org/wiki/Hellbanning" rel="nofollow ugc">shadowbanning</a> (or hellbanning) for comments.
Comments by shadowbanned users will be invisible to all other users. However, the shadowbanned users will continue to see their own comments, hopefully oblivious to the fact that they’ve been shadowbanned. This is non-destructive in that changes are not made to the comments themselves. Shadowbanned comments are still saved to the database and visible to admins in the dashboard comments listing. Note that contrary to other plugins, Marktroll does not expect the commenting user to be logged to be shadowbanned.
If you disable this plugin, showbanned comments will become visible to all users.
Licensing
All code is released under The GNU License. Please see LICENSE.txt.

MarkTroll

MarkTroll is a WordPress plugin that will let you shadowban (hellban) any unlogged (regular) commenter on your blog.

WP-BlockYou vs MarkTroll