The Deep Web is a goldmine of information, and since the Deep Web is larger by far than the parts of the Web we can access with a simple search engine query, there's potentially much more information available. The following resources can help you delve deep into the Deep Web, making your people searches even more rich, detailed, and authoritative.
If the person you're looking for has ever created a website, you can look that website up via the Wayback Machine, a database of over 150 billion pages archived from 1996 to the present.
The American FactFinder offers population, housing, economic, and geographic data for any community in the United States. You can use this database to dig up information on your person's community, schools, and other demographics.
You can find a zip code here by using an address, city, and company; they also give you the option to find all cities in a particular zip code.
Evri is a fantastic source for tracking down traces of activity on the Web. Simply type in the name of the person you're looking for, and Evri will return anything that mentions that person: blogs, newspaper articles, Twitter, and a lot more.
Pipl is specifically designed to dive into the Deep Web for information. It retrieves results from databases that don't come up in regular search engine queries.
6. NNDB Mapper
The NNDB Mapper traces connections between people graphically using an interactive map. These connections could be family-related, corporate, political, etc.
MyDanwei specializes in organizing corporate-related information on both companies and people. Type in a name, and you'll get detailed background information such as salary, past positions they might have held, who they report to, and who they work for.
MelissaData Free Lookups offers you a wide range of free tools you can use to plumb the Deep Web for people search information, including Canadian addresses, house numbers by zip code, IP location, local school information, income tax statistics, and much more.
FamilySearch is primarily a genealogy tracker, which makes it an invaluable people search tool as well. Type in as much information as you know, and FamilySearch will bring back birth and death records, parental information, and more.
MyLife retrieves information from a wide variety of social networking profiles, proprietary web sites, and public records. You'll have to register to see detailed information (it's free), but the results are well worth it.