Hotmail lets you have a few anonymous, semi-disposable emails which get forwarded to your main email, while keeping it secret. You can add and remove them as you see fit.
Gmail lets you do two things...it ignores the period "." and it ignores everything after a plus "+". If your Gmail is "robot123" you can give someone "ro.bo.t1.23+extra" and it will get sent to you, while keeping your real email hidden. You can use this to track cookies. Give (for example)
www.cnn.com your email as "robot123+CNN" and you can tell exactly who they sell the email to, if you get emails from other companies sent to "robot123+CNN". Now, this isn't quite as anonymous as the hotmail one, since you're core email address is basically in the other ones, but it's east to use.