Here are a couple of email utilities to deal with annoying websites asking for an email address for no need at all:
First is Mailinator . There is no signup, no passwords. Just give out any email@example.com and then go and check the email on mailinator. No password. Basically your email address is your password! The emails will get deleted after "some" time. Amazing piece of work! However, the spammy websites get smart and start rejecting anyone registering with mailinator.com address. But mailinator gets smarter: there are many other "mirrors" for mailinator that you can use. fastacura.com, fastnissan.com, fasttoyota.com etc. Each of the domains forwards the email to mailinator.
Second is Jetable which can act as a limited-time email forwarder. You enter your real email address and enter time limit 1-8 days and it gives you a new address (something like firstname.lastname@example.org) which is valid (and forwards email to your real address for the specified time).
I kind of see the value in jetable.org, but who is to guarantee that jetable.org won't start spamming your real email address ? The issue with mailinator is that of privacy (which is countered by using obscure email address). e.g. md5(string). Another issue is about the mail getting deleted. People have stepped up to solve this problem as well! There is a utility to keep scanning mailinator and forward any received email to your real email address from your desktop. Look here!