Have you ever wondered if there is any other plugin like Akismet but thought that maybe na there isn’t well then you were wrong because their is and its called Mollom, many people know that Akismet is not for them so they were looking for an alternative , so i can say your searches are over because of Mollom.
Mollom basically has all the features that Akismet has but one feature that Ak doesn’t and its when Mollom is unsure of a message, it presents a CAPTCHA to the user and if they pass, the comment gets pushed into the moderation queue, if they fail, the message is automatically deleted.
Before it was only available to Drupal and now they decided to move it to WordPress and we all know why ( bigger market ). Here is a video to explain it better to you:
The Plugin has a free version and a premium one just like Ak.