The referrerRemover plug-in already does a great job of getting rid of 'Referrer' SPAM.

Now I've finally got rid of comment, message and trackback SPAM! Woo-hoo.

How? Via the ManilaAkismet plug-in. Read all about it here. Basically, it is a spam filtering service created by Automattic. Akismet attempts to filter link spam from blog comments and spam TrackBack pings. The filter works by combining information about spam captured on all participating blogs, and then using those spam rules to block future spam.