Sender Policy Framwork (SPF) is an excellent protocol for eliminating SPAM. It works by eliminating the ability of spammers to lie about who they are. No longer would you receive email from a spammer claiming to be your bank. The beauty of it all is that once spammers can no longer pretend that they are sending email from known good domains, they will be forced to send from their own domains. At that point we can only accept email from known good domains, and be SPAM free.
The best part is that it is actually catching on; check out the early adopters list.