From Facebook Developer Wiki

It would be nice if this list were tiered by how popular the website are

It's a wiki, so if someone wants to volunteer to track the page ranks of each site and adjust this page daily, they're more than welcome to do so. :) It's ostensibly alphabetical, tho that breaks from time to time as people add their sites. Pete (563683308 10:46, 22 June 2009 (PDT))