I’ve started using the Bad Behavior/Bad Behaviour plugin for WordPress, which is meant to cut down on the number of spambots that attempt to access my site. In theory it shouldn’t block any real visitors, although this has been known to happen, so if you notice any problems (e.g., can’t get to my blog from a feed, or from a link or search), please let me know. The plugin has been installed a week and nobody’s reported any problems so far. It works nicely with Spam Karma, the spam blocker I use.
I can recommend this plugin based on my experience so far; I’ve noticed the amount of spam that I get is much less, which means that I will be able to check the Spam Karma logs for any real comments that were inadvertently caught. If you’re plagued by spam bots on your blog and you have some control over the environment, it might be worth trying out.