I suggest using the ReferenceUSA database, which in your area is available on one computer in the Science, Business and Social Science area of Oakland Public Library's Main Library, according to their databases page.

When I do a Guided Search for these kinds of businesses in Oakland, I get 37 results. In order to replicate the search, you need to enter the SIC code of 609903 in the Business Characteristics tab and Oakland, CA, in the Geography tab. A SIC code, by the way, is a U.S. Department of Commerce-defined industry classification code (try putting in keywords like "check cashing" and "payday" into the Yellow Pages heading search box, and you'll find that the main results all fall into this code).

The individual records for each of the resulting business listings give a lot of information you wouldn't find in the Yellow Pages. For example, the record for the Check 'n' Go at 10327 International Blvd indicates that a Ms. Harley Huggins is the owner. ReferenceUSA will also tell you if a business is part of a "corporate family."

I'm not sure what kind of research you're doing, but you might be interested in the following articles, among others on this topic:

• "The Next Frontier for Economic Justice" by Gabriel Thompson
  Colorlines, Spring 2006
• "Check It Out; A lawsuit against payday lenders seeks to bankrupt the industry" by Gwen Shaffer
  Philadelphia Weekly, Dec 28, 2005-Jan 3, 2006
• "Check for cheque-cashers; America's money-transfer business" (full text available via databases your public library may subscribe to)
  The Economist, January 13, 2007