Based entirely off the "Server" header from requesting the "http://www." form of the server and following all redirects.
Omitted from the results are duplicates in alexa that are effectively localisations of other sites in list list (e.g. amazon.co.uk is not included because amazon.com is, similarly for google.de and bing.co.uk, ebay.jp etc).
Warning: Before doing this yourself - not all of those URLs are safe for work!