The North American Industry Classification System (NAICS) is the standard used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy.
NAICS was developed under the auspices of the Office of Management and Budget (OMB), and adopted in 1997 to replace the Standard Industrial Classification (SIC) system.
Here's a quick and easy way to search for companies by SIC codes using MergentOnline- get an extensive list of private and public companies sorted by Industry Code- http://screenr.com/tXJ8
There are several new Industry databases on this list. Give them a try!