<rubs butter all over himself...>
Gleym wrote...
What about a captcha?
Mollom incorporates captcha as well as textual analysis.
Generally, I set up the captcha only for registration or anonymous comments and allow my registered users to bypass captcha. They (and I!) do not bypass the text analysis, however. Which reminds me, I should turn comments on...
And basic usage (for not terribly busy sites) is free.
<...and slips away>