You can do them by IP addresses. John Chow uses WP-Ban to prevent comment spammers reaching his blog by banning their IPs. I dunno if this is what you’re looking for…

http://www.johnchow.com/ban-those-blog-comment-spammers/

It would be hard to completely stop one individual from visiting your site, but there are methods that (I think) use the .htaccess file to disallow certain IP address from visiting a site. If I were in that sort of situation, that would probably be the easiest way to do things. Alternatively, you could password protect the entire website and only let people who know the password gain access, although this would cut down on the amount of traffic you get in general.

I have used WP-Ban on my Wordpress blog and the “Troll” module on my Drupal site to block individuals by IP.. that works good until they realize they can use a web-proxy to come back and harass you even more.

To deal with proxies i use a combination of the BadBehavior plugin for both Wordpress and Drupal, combined with CSF. In CSF I have a block list of over 1,000,000 web-proxies and compromised servers. Although it’s still possible to find a proxy that’s not in my list, it takes a LOT of work..

Yeah, I wish we could do it on blogs, just like you can do it with forums, but I dont’ think that there is a way to do it.