I am polishing off the last of a Spam plugin (Montyspam) after 3 months(!) and I'm looking for one of two people to act as Beta testers.
Montyspam is Bayesian spam filter - i.e. it statistically works out the probability that a comment or post is Spam or not. So far on my site it has proved more than 99% effective. It has proved pretty much immune to spammers techniques such as random words etc. In fact, it works so well that on my site comment spam essentially is defeated.
It's designed to be as easy to administer as possible. Essentially an administrator simply has to manually classify messages that Montyspam regards as 'difficult to classify' which is rare anyway. Because the Bayesian filter 'learns' there are basically no complicated settings. It's also designed to have a minimal impact on legitimate users. So neither the site admin or your users have to go through dozens of messages to check whether they are Spam or not, and there is no Capcha.
If anyone is interested in trying it out could they put a message here. At the moment I'm really looking for a just a few Beta testers for feedback and suggestions. You do need at the moment to alter one line of the Wordpress code (so that a menu appears in the Admin area).