The 'exact' link I clicked was this one:
Code:
http://aws-portal.amazon.com/gp/aws/developer/account/index.html?action=access-key
I hadn't been signed up when I clicked that, so it prompted me to create an account.
I assume it's the same thing as going through the front door and clicking the 'sign up now' button, as the pages look identical:
http://aws.amazon.com/ - click 'sign up now'