UPDATE: The developer of the site has since taken the site down after I had already written the article. Thanks to everyone who sent emails and posted comments letting me know!
There are all kinds of free services out there that will help you create a throwaway email address, but TempAlias stands out a little with its implementation. With TempAlias they generate a random email address that will forward mail to your real email address. Then you specify how long you want the email address to be valid for in terms of days or number of messages received. Pretty clever.
After you hit the Generate button you’ll instantly be given the alias you can use, but they also go one step further to make generating an email address even easier in the future. If you look closely they actually provide a bookmarklet that can be used to generate an address using the same settings you had entered in. Basically that means in a single click you can have a completely random email address ready to be used.
P.S. If you’re looking for something similar to this that doesn’t forward to your personal address I highly recommend checking out 10 Minute Mail.