SPAM defender for WordPress - no spam comments, no spam registrations, no spam contact emails, no spam trackbacks.
The free version gives you up to 5 comments that are not spam a day. While typically I have less then that, I do have post that get more then 5 real comments. They then go into manual moderation, with the rest of the spam.
I didn't test it further as I wasn't willing to register just to test it out. If I can't find anything better maybe I will.
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