I've added a few more sites for IdentiFight to search, plus links to some of the people-search sites mentioned in Liberate Media's 12 social media tools to find people online.
Also, after finding URLs from each of the known sites, IdentiFight now passes those URLs to Google's Social Graph API, which returns any other URLs that are known to be linked to the original set. These are often homepages, blogs, and sometimes accounts on networks that don't allow search by email (usually self-declared using rel="me" links).