An ounce of prevention is worth a pound of cure.
Spam is annoying, and there are certainly a lot of WordPress plugins that can help you catch it, moderate it and delete it. Several useful spam catching & killing plugins include Akismet, Bad Behavior and Sparm Karma 2. I have used all of these plugins, and all three are pretty effective in catching legitimate spam comments.
But instead of worrying about catching spam, focus on preventing it. Imagine being able to write about lab coats and not get crappy spam comments! There are several ways to accomplish this, including requiring user registration in order to post comments, common sense and math questions, and some basic captcha (mixture of letters and numbers that are randomly generated) questions. But these can all be bypassed by spammers who use bots to make the rounds on blogs.
So, what can work? Consider using reCAPTCHA. Unlike a typical captcha, reCATCHA works by using scans of digitized books. These scans cannot be read by a computer or spam bot, but they can easily be deciphered by human viewers. Additionally, reCAPTCHA uses two words or groups of words together in one puzzle/question, as a further preventative measure against spam attacks.
reCAPTCHA is put to use by PayPerPost (which is where I first saw it) and many websites that allow user account registrations. Now it’s found in a plugin: WordPress’s very own WP-reCAPTCHA. Installation takes less than five minutes (upload, activate, fill in the API keys which are given to you with a free account registration at recaptcha.net), and the reCAPTCHA box is automatically displayed on a blog entry’s comments page. Additionally, the plugin allows the reCAPTCHA functionality to be used with new user registrations.
You can see WP-reCAPTCHA in use right here.
Bottom line: be proactive, not reactive.
