The Security Mentor

Unless they're going to mail you a receipt or a password, they don't need it except to send you junk. But their forms always require it. My favorite solution is to fill in me@privacy.net where they ask for my email address. If they send email there, they get back an automatic nastygram suggesting that they should offer attractive products instead of sending junk mail.

Suppose some merchant really does need to send you a receipt, or a password, or a web address where you can download their product. Suppose you don't trust them with your email address (OK, but then why are you buying from them?). An outfit called Sneakemail lets you create a new address for every place you do business with. The new address is something like wi3gb4j@sneakemail.com, and mail sent there goes to your real email address until you want it to stop. You can cancel that one address if you start getting spam through it.

The sneakemail web site is kind of bare-bones. The real information is in their Frequently Asked Questions page. They're free for basic usage, with some extra goodies if you pay them.