I use Conditional Captcha
with Akismet. You have to use Conditional Captcha in conjunction with Akismet or another spam blocking program - it does not work on its own.
Here's how it works:
1) Akismet asks "is this spam?" If Akismet determines that the comment is not spam, it is let through (or held in moderation, depending on whether you are moderating comments) If Akismet thinks the comment IS spam:
2) Conditional Captcha says "fill out a captcha." If you fill it out correctly, the comment goes through (or to moderation). If it is not filled out correctly, the comment is trashed.
What this means?
- MOST of your commenters will never see a captcha. If Akismet doesn't think they're spam, they will never know the difference.
- Legitimate comments will never
get caught in spam. If someone is flagged as spam but then is able to fill out a captcha, the comment goes through. Therefore, you don't have to spend time looking in your spam folder for real comments.
Since I have installed this, I have gotten NO false positives (no legitimate comments have been sent to spam filter) and very few spam comments have gotten through.