Last year, Alan Masarek made news as he left Google to become Vonage’s new CEO.
AnyWho - AT & T's Anywho. Search by business category.
Bell South - Bell South Yellow Pages and business directory, south-east US. (Now this is just a general, yellowpages site.
Business Yellow Pages - National yellow pages with more than 10 million businesses. Requires state. Has map links, search by street, and reverse search.
Feist Online - Regional yellow pages publisher, covering most of Kansas, Western Oklahoma and West Texas.
Feist is now owned by yellowbook.com; it was acquired by yellowbook.com back in 2004. So, this link is a little dated, but we'll keep it for posterity's sake.
Infobel - International/National Yellow pages; Search by business category; infobel used to have a feature that allows you to find businesses nearest to a specific address or from a city center point.
McLeod - Regional yellow pages, mostly midwest. 2010: Now defunct.
sbn.com - Another national yellow pages. Seems a bit inaccurate on categories. For example Citibank is listed under "Government". 2010: A rather prescient observation, eh?
Smartpages - Yellow Pages and business directory from Southwest Bell, Pacific Bell, and Nevada Bell. Now owned and operated by yellowpages.com.
Superpages - National Yellow Pages. Incorporates the former site Bigbook.
Switchboard - National business white pages including search by category. Has "search near" feature.
U S West Dex - US West Yellow Pages and business directory, north west US. Now, no longer in existence.
WorldPages - Another national yellow pages, now owned by yellowbook. Acquired by yellowbook in 2005.
Yellowpages.com - This site is popular (because of the name), but seems more inaccurate than most to me. For example, searching for Commercial Banks in San Francisco produces (at the time of review) companies like "A1 Window and Blind Cleaner" and "Big Bob's Water Delivery"!
Infospace - Nationwide Yellow pages. Can't do multistate search, but can search for places near a location or by pointing on a map.