Ad Age Datacenter
http://adage.com/datacenter/
“100 Leading National Advertisers” & “Top 200 Brands” are just 2 of over 100 rankings found here. Includes advertisers, marketers, brands, ad agencies, salary surveys, and other rankings from Advertising Age magazine.

ClickZ Network (formerly: Cyber Atlas)
http://www.clickz.com/stats
Internet usage patterns, demographics, and other statistics on web advertising.

EASI Quick Reports & Analysis
http://www.easidemographics.com/
Demographic data culled from U.S. Census Bureau & other government sources. Reports contain various statistics for each geographical area including general population, employment, industry, owner/renter, and other data. Reports can be compiled by various geographic regions including by city, state, TV market, zip code, & others. Requires free registration.

Entertainment Resources & Marketing Association
http://www.erma.org/
database of members providing product placement for brands in films and television programs. Searchable by agency, brand name or advertiser, & industry.

U.S. Census Bureau
http://www.census.gov/