Spam Karma was one of the first plug-ins that I ever installed on a WordPress blog, after finding it recommended on a forum called “Notes from Spain“.
I like the fact that I can fine tune the spam detection settings, but also that I can find out why the comments were blocked.
It is a shame that Spam Karma is no longer being updated. But if need a good alternative to Akismet, then it is still worth taking a look at.
Download link: Spam Karma Project