Mailinator
In our internet world, you often need an email address NOW. Signing up for an email service takes time - that's probably ok for most emailing, but every now and then you need a quick email address for just a single email. After that you don't care what happens to it. Given that such disposable email is ready at your disposal, you can avoid giving out your real email address when you are afraid of getting spammed. Instead, make up any address @mailinator.com on the spot and go check it later.