Central Opt-Out Database
A concept that will only work if a ton of people sign on and the bulk e-mail senders play nice, but a good idea, nonetheless. From the site:
The Central Opt-Out Database was designed to give end users a central place to opt-out of unsolicited e-mail distribution lists. We provide e-mail distributors with a list of unreversable e-mail address fingerprints in MD5 format. They can then compare this list to their own e-mail lists and remove matching addresses. This results in less unwanted e-mail for registered users, and less complaints for e-mail distributors. Participation is voluntary on all sides, and it is our sincere hope that e-mail distributors will see the value of removing from their lists those people who have specifically said they do not want to receive unsolicited bulk e-mail.
I just put on about 20 e-mail addresses. And some one has already created a comparison script for e-mail senders.