Yahoo mail has a feature under Mailboxes, called "Disposable email address" that allows you to pretty much do the same. You choose a "base" name, and then you can create upto 500 disposable addresses of the form basename-keyword@yahoo.com - you can choose the "keyword" based on the site you're signing up for, the basename stays constant. All mails to the disposable address get delivered to your normal mailbox, but you can go and delete a disposable address or filter it to spam. Also, both the basename and keyword remain untraceable to your actual address (unlike gmail's + format that has your base email id embedded in it).

I used to use this earlier, but then I couldn't find the setting easily on their mobile web interface and got tired of either switching to the desktop version or waiting to get to a desktop to complete a signup. Nowadays, I just report spam if there's no unsubscribe option.