Mailinator - Any Inbox. Any Time.
AnyMailFinder.com - Find anyone's email address
Guerrilla Mail - Guerrilla Mail is a web-based app that provides a disposable and anonymous email address. Users of the service are not required to set up an account in order to send or receive emails.
Hunter - Find all the email addresses related to a domain
Spamgourmet - spamgourmet provides email addresses that get created automatically the first time they are used, forward messages, and then automatically expire.
EmailMatcher - Find anyone's email address in a matter of seconds, for free