I use
sneakemail.com when I register for anything on line. Sneakemail lets you create "disposable" email accounts, so what you do is create a unique address for every registration. Every email you receive from that site is tagged with your name for them, so you always know "which" web site was responsible for sending you the crap. If one of them does become "spammy", you just tell sneakemail to block it, and it's done.
Sneakemail offers a free service which is just as good as the pay service, but the subscription is only $24/year, and I figure it's been worth it to me. I've used them for several years now.
The drawback, of course, is that someone at Sneakemail.com could be reading your email. Up to you if you want to risk that, but I figure for most "shopping" signups, I don't care too much. (I used my real email for paypal, so Sneakemail wouldn't see that password.)
I will say that virtually every web site I've ever signed up for has done a good job at not spamming me (I make sure to always check the "don't share my email address" boxes, of course.) No site wants to be identified as "the site for getting SPAMMED," so they all try to protect their lists.
I have discovered one place where my email address has leaked out into the world, however. Chain letters. Ever get one of those "send this to 20 friends or an angel will smite thee" pieces of crap? What happens is one of the recipients thinks it's soooooo cute that they post it, addresses and all, on a web page or in a news group. Spammers LOVE those, they're just filled with nice juicy addresses of gullible people. Unless you really like those things, ask your friends nicely to not include you in their "list of people who get email jokes," or better yet give them a separate sneakemail address. Then you can let them know if that's where your spam came from.
If you have any questions, you can email me at f58kbf802@sneakemail.com and I'll be happy to answer them. Ask quick because when the spammers harvest this address, I'll just shut it down!