Defensio claims their solution will "end annoying comment spam." Unlike many one size fits all solutions, Defensio customizes itself to a particular blog and the preferences of the author(s). In short, it treats a particular post on one blog as spam, whereas on a different blog, it might be viewed as "ham" (i.e. not spam). It also offers a sorted list of spam based on "spaminess" value to make it easier to sort out the ham from the spam.

Defensio offers plugins for wordpress, MoveableType, and 5 other blogging platforms. For non-commercial blogs, it's free. For commercial blogs, there is a nominal monthly service charge. "Commercial" use is primarily determined by the number of comments filtered in a month as well as "money" made by the blog.

Personally, I find the combination of Akismet and Spam Karma 2 quite sufficient on my WordPress-based blog. However, it's nice to see some competition out there.