Akismet is the comment spam cop that WordPress.com uses and it works great. Though this is not a high-traffic site (even if you’re on drugs) I do get spam popping in to say hello every once in a while. Akismet seems to block comment spam quite nicely and I’ve not had to manually delete comments, except the occasional one that’s bound to get through.
Here’s Akismet talking about themselves:
We can’t stand spam.
Who can? You have better things to do with your life than deal with the underbelly of the internet. Automattic Kismet (Akismet for short) is a collaborative effort to make comment and trackback spam a non-issue and restore innocence to blogging, so you never have to worry about spam again.
If you’re on WP.com you don’t have to do anything, since Akismet is already installed and running. If you’re on some other platform though, you might want to consider using Akismet.
Check out more at their website: http://akismet.com/