If you're using firefox you can download the "Bloody Vikings!" addon which creates a random 10min mail with any of a number of services.
If not lemmi list a few services:
10minutemail.com
anonbox.net.
dispostable.com
mailcatch.com
mailforspam.com
spamavert.com
trash-mail.com
koszmail.pl
That's all I could find right away
If you want a more permanent service that's pretty secure i'd go with hushmail, they have alot of features including signing mails and types of encryption.