In addition to putting legal research tools at your fingertips, Lexis and Westlaw also have a wealth (pun intended) of business resources.
On Lexis, go to the News & Business tab and look at the Company & Financial and Market & Industry categories. You will find great directories for companies such as Hoover's and Standard & Poor's, as well as the Directory of Corporate Affiliations - where you can find out exactly who owns whom.
On Westlaw, set up the Company Information tab using My Westlaw and then investigate the great company resources - Hoover's, Standard & Poor's, and SEC EDGAR filings. Don't miss Brands & Their Companies - to discover exactly who owns your favorite brand of tuna fish. (Hmm, tough choice - they are all soooo good. ;)
Ernster, the Virtual Library Cat
Above the Law - A Legal Tabloid - News, Gossip, and Colorful Commentary on Law Firms and the Legal Profession