While googling around before our Easton visit I came across this link which described a mall close to the hotel we were staying. I was impressed with the demographic information that it provided for prospective tenants - mainly income and household counts within 3, 5, and 10 mile radius. My guess is the data came from Census.
It did remind me however, of another interesting bit of data that I came across while working on a project. This was the PRIZM Claritas market segmentation data. The household categories (by address/zipcode, I think) were quite entertaining to read.
If you use this link you can enter your zip code and find out who you are. The full list can be found here and the categories read like this: Upper Crust, Blue Blood Estates, Bohemian Mix, Money and Brains, Movers and Shakers, American Dreams (established urban immigrant families), Gray Power (affluent retirees in sunbelt cities), God's Country (executive exurban families), New Empty Nests (upscale suburban fringe couples), Young Digerati (tech-savvy young singles and couples), Shotguns and Pickups (rural blue-collar workers and families), City Startups, Middleburg Managers, Mobility Blues, New Beginnings, and Up-and-Comers.
It can also provide the following information - Money and Brains cluster is described as those with "High incomes, advanced degrees and sophisticated tastes to match their credentials." They tend to shop at Nordstrom, support the arts, read Business Week, listen to all-news radio, and drive a Jaguar. With this type of information, marketers can target their product to those who are most likely to buy.
I peeled the above from About.com. Wikipedia also provides a full list.