I usually use a unique email address for each corporation I do business with. For example, all e-mail from Ameritrade went to amer@galexander.org. I notice that a few companies will give your email address to outside parties in violation of their privacy agreement. I am shaming them here.
From early 2006 (earlier?) to mid 2007, Ameritrade had repeated compromises of their list of email addresses. I received a lot of stock advice spam (fraudulent "insider tips") because of this. They refused to acknowledge the problem, sending out a ridiculous (and deceptive) form letter to users who complained about it. Then they would give your new address out. It was terrible. They recently declared the problem fixed, and maybe it is. But despite the sensitive security nature of their operation, they refused to address this problem for more than a year.
Shame!
The address I've only used for interactions with Sprint customer support is now receiving spam from a housing market website of some sort.
Sprint deserves an entry here anyways just because they kept on calling me in the weekend mornings to tell me that for only $20/mo more I could have two phones. But that's another story.