Temporary emails expires every 15 minutes

corsa

http://www.guerrillamail.com/

Great so you dont get spammed etc they close every 15 mins or if you need them for longer you can click the option give me another 15 mins.

SqueakyRat

Not to steal your thunder, but 10minutemail.com is another good one for registering on websites without fear of being spammed to death !
As the name suggests these email addresses are terminated after 10 minutes but gives you the option of keeping it for a further 10 minutes if the email you want hasn't arrived in the 1st 10 mins . In theory you can keep it as long as you keep hitting the "Give me another 10 minutes..." button.

thepearce

https://www.spamgourmet.com allows for a preset number of mails to be forwarded. Can be increased.

martyn4764

And http://www.jetable.org allows you to choose how long the generated email is valid for (an hour, a day, a week or a month).

3BADDICT

I use www.bugmenot.com which keep your emails for up to 24 hours.