I used to use endjunk.com a few years back and just started using it again. It's a great way to find out who's selling your e-mail address.
What you do is you pick a username, for example, whter. Now, you are provided with an e-mail addy of [email protected] that will forward all e-mail to any e-mail address you specify --the setup is basically a catch-all setup. So...let's say you want to signup for a newsletter, for example, TigerDirect.com's newsletter. Perhaps you're suspicious of them for whatever reason, so in the e-mail address field, you put [email protected]. Now let's say that they gave your e-mail addy to a few SPAM'ers for some extra bucks --you will now know if they did, because if you see any other e-mail, other then TigerDirect ones, go to [email protected], then you know they sold you out.
You can basically put anything in front of @whter.endjunk.com. Usually, you would want to put something that would remind you of who you gave that e-mail address to, to make sure they don't send you unsolicited e-mail. If they happen to do so, you can always just block e-mails to that particular address.
Just thought I'd share something I recently started using again, in my defense against SPAM.