I posted yesterday about the comment spam catching WordPress plugin, Akismet. There are other options.
One that I have used and found very effective is Spam Karma 2. The onsite overview states:
Spam Karma 2 (SK2) is an anti-spam plugin for the WordPress blogging platform. It is meant to stop all forms of automated Blog spam effortlessly, while remaining as unobtrusive as possible to regular commenters.
Andy Roberts has an instructive commendation for Spam Karma 2 in a post from last August, Instant Karma for Comments and Trackbacks. Like Andy, I appreciate the fact that with Spam Karma 2 you can “see under …read more

Just as email spam is a scourge of email and a serious hindrance to clear communication via email, comment spam is a scourge of blogging. Businesses getting into blogging need to have some confidence that their site will not be polluted by this comment spam garbage.
A standard plugin for WordPress, the Automattic Kismet, or Akismet tool seems to me to operate very effectively as a spam catcher. I’ve been quite impressed, with this and otherr WordPress blogs of mine, that the various spam messages don’t seem to be getting through. And I have been quite pleased to hit the ‘delete all’ …read more