Spokeo ™ “Spokeo is a search engine specialized in organizing people-related information from phone books, social networks, marketing lists, business sites, and other public sources.” NOTE: Spokeo Initial search brings free data; further is offered for a fee.
rootsweb Social Security Death Index (SSDI) A Basic Search “...by entering one or more fields in the form...” And an Advanced Search to add state, birth year, and more. Close to 90 million records.
Checkdomain.com Use this site when you come across an e-mail address and it's not apparent what organization it goes to. Be sure to include the ".edu" or ".com" or other extension with the address.
Google Groups (formely Deja News) Is a search engine to search Internet Usenet news (discussion) groups for prople who have the same interests as you.