Many people find ranking lists helpful to understand a company. Sometimes it is because of what or how the list is ranking companies or sometimes just because of the information included.
Some of the most helpful ranking lists can be found in trade publications because they publish lists of "the top" or "the best" that are most appropriate for their readers. These lists can be helpful for understanding the overall landscape of the industry as well as identifying competitors. Often these lists present information and data that can't be found elsewhere because they know their readers' needs and what their readers expect.
Since there are so many of these types of lists they cannot all be included here, but a few of the more notable ones have been included as examples.
Many full-text databases include articles from industry-specific magazines that contain lists/rankings. For example, Gale's Business Insights: Global, which focuses on large public companies and is often found in public libraries, includes a link to various rankings from their Business Rankings Annual where that particular company is mentioned.
Beyond those ranking lists created by publications, there are ways to create a more customized list in many of the databases that provide company data. Many rankings and lists of companies within a certain industry or geographic area can be created in databases which allow researchers to choose which items they want to search. For instance, a researcher can choose a particular industry by using NAICS/SIC codes and limit that list to a state or states. Then the resulting list can be sorted on sales.
There are ranking lists that are not specific to any particular industry - two of the most obvious are from Fortune and Forbes. Some focus on a particular geography others on specific themes. They can be useful for those trying to understand the nature of a company and tell you information not always evident but are often helpful just as general background. For example:
Various trade publications and associations often publish special ranking lists that are particular to their industry. This is important because they are produced by people who have knowledge of the industry and for people in the industry and what they want to see. They rank in ways that are appropriate for that industry and often include information that is relevant for, and specific to that industry. That can be helpful for those looking to understand the company within the industry. Many have an Internet presence though it varies what is made available for free. Here are a few examples: