If you need an email address to register on a website, but don't want them to bombard you will possible spam, a disposable email address is the answer.
The following services create an alias address. Each have varying life-spans and some allow you to decide that time.
10 Minutes Mail
As the name suggests, your email address lasts for just 10 minutes.
My Trash Mail
Use any of the sites domains for as long as they stay active.
Your email address can last from anywhere between 12 hours to 3 months.