I'm basically blocking everything with an .ru (Russia) or .ua (Ukraine) extension. Notoriously bad sites, though, include Bigmir.com and Lviv.net. Luckily, most of the spam sites are pretty easy to recognize by name.

I do permit commenters from select countries as the above, but also including .cn (China), to sent me a direct message indicating that they are not a spam bot if they wish to register and/or comment. I can't really stop the bad links beyond what my blogging software permits, though. And the scrapers? I'm happy to hear whatever you've got to say on how to reasonably stop them.