I noticed my sites appeared on their own so I think it is based on alexa traffic for the site's category. However do not quote me on that since I am only taking a guess. The Funender site is listed 4th on Unsigned Bands page: http://www.alexa.com/browse?&CategoryID=1959 EDIT OK here is the answer it looks like their directory is pulled from DMOZ listings: http://www.alexa.com/site/help/?index=87
I have sites not listed on DMOZ but show up in alexa search results. I think they are more like dogpile.com
Well that is what it says on their Alexa site if you view the link I posted. Question Can I add my site to Alexa's directory? Answer The directory on Alexa.com is a copy of the Open Directory Project, located at www.dmoz.org. The Open Directory Project contains over 4 million sites in over 590,000 categories. The directory is maintained by over 73,000 volunteer editors around the world. To add your site to the Open Directory, go to www.dmoz.org, find the category your site should be listed in, and click the "Add URL" link at the top of the page. We highly recommend reading their submission guidelines first at http://dmoz.org/add.html.