I was using the commercial databases available to me at SLU’s online library portal (you need to be part of the SLU community to get access, but you may have access to an online portal through your own local library, or through an alumni account to your alma mater), and found that information available on companies differed quite a bit. From the perspective of a person doing research on small, privately-held firms, here are some important differences among three databases.
LexisNexis Academic: Look for listings for your target company under “Company Directories & Profiles” or “Business & Corporation Information”. Specific databases of interest will be “Zoom Company Information” (good for size, leaders, contact info), Experian Powered Business Data (good for Zoom’s info, SIC code, sales, credit level and performance, UCC filings), and VeriGift (for charitable giving).
Mergent Online: The default checked databases are fine for larger businesses. For small businesses, use the “D&B 20 Million Plus Private Company Search”. The result is a rundown of contact information, SIC code, leadership, size information (sales and employees), and a list of suggested competitors (which you can adjust by state). This is built off of the D&B Credit Reports, so it is generally based on reports by the firms themselves.
PrivCo: PrivCo really focuses on high-potential businesses, and has about 1 million firms in their database. The academic version (which SLU has) gives contact information, industry and funding rounds and any VC or M&A activity. Note that much of this information is available for free from CrunchBase.com.