[Plugin: Conditional CAPTCHA for WordPress] At last

I network installed this plugin yesterday (some 16 hours ago). I was getting tired of deleting spam from all network sites every day. I had Akismet, Bad Behavior and First Defence Against Spam (blocking over 80 IPs!) running and still I had up to 40 spams a day for some sites. I started to look for a Captcha plugin, even though I dislike these things, but this combination with Akismet (only a Captcha when Akismet says a comment is spam) is perfect. After 16 hours, one comment made it to the spam queue and about 80 were deleted by this plugin. Goodbye spam queues, at last.

http://wordpress.org/extend/plugins/wp-conditional-captcha/