Every now and then I want to access content or a service on a Web site which requires registration with an email address (for example, live365.com started requiring registration a couple of days ago, and many online newspaper Web sites do this). I used to always give a fake address, for fear that the site will sell my address to spammers, or that the site will send me a bunch of promotional junk I don't want. But that doesn't always work. Sometimes the site requires a valid address so that they can send me something that I need to complete the registration. In this case, mailinator.com is a good way around this problem.
If you go to mailinator.com, it auto-generates an email address for you in the form of firstname.lastname@example.org (you can also make up your own), and you can give that address when registering for the newspaper (or whatever) Web site. Then just go to mailinator.com and check for mail sent to that address. There's no username and password, so you wouldn't want to use it as an actual email account or for anything confidential (anyone who knows your mailinator address can read your mail). But it's a good throwaway email account, so that you don't have to give your real address.
(In fairness to live365, they don't appear to have sent me any mail at all after registering.)