Mailinator - Any Inbox. Any Time.

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.

MailDrop - maildrop is a Mail delivery agent used by the Courier Mail Server. The maildrop MDA also includes filtering functionality. maildrop receives mail via stdin and delivers in both Maildir and mbox formats.

Spamgourmet - spamgourmet provides email addresses that get created automatically the first time they are used, forward messages, and then automatically expire.

TrashMail.com - Create a free disposable email address! Its really easy to use:

AnonAddy - Create unlimited aliases for free. Protect your email from spam using disposable addresses. Encrypt forwarded emails with PGP encryption using this service.