Spamgourmet
From the “Dear God, that’s so simple. Why didn’t I think of it?” file: spamgourmet. James Cridland mentioned it on UKNM, so I’ll just use his description:
Let's say I enter a competition on British Gas's website. When it asks me for my e-mail address, I don't write my "real" one in - I write in britishgas.5.jamescridland@spamgourmet.comThis then bounces THE FIRST FIVE messages from them to my e-mail address (amending the header to say how many are left). , and eats the rest. If I like what I’m getting from British Gas, I can let them send me more messages, too, if I like. If they sell my e-mail address to someone else, I’ll be able to tell, too.
And the best bit? It’s free.