Tom Raftery has an interesting blog entry on how use your web server’s .htaccess configuration file to help reduce the amount of comment and referrer spam your WordPress journal receives.
While Tom uses the excellent WordPress plugin Spam Karma to protect his page and provide information to assist in his spam monitoring, his advice on how to use your server’s own filtering features will work with most web sites, regardless of content.
The developer of Spam Karma also has another tool called Ref Karma that works along similar lines and can be used to protect most websites with a spot of PHP scripting.
None of the advice above is overly complicated, but does involve some experience with scripting and server configuration, so be prepared to do a little background reading if this is new to you.