Its hard to keep up with all the company information sites. Typically, they provide useful free information and require payment for the valuable corporate nuggets, particularly contact information. Hoovers is the gold standard and made its reputation with their humorous but sometime banal business summaries. I like Manta because they provide revenue data for free. Jigsaw is another one and they’ve just added a tab called “research” which appears to collect web-based information from blogs and social media sites like Facebook and Flicker as well as Google news. Its useful and easy-to-use.
The thing to remember is there is no one-stop shop for real research. If you want very basic information, its fine to check out of any of these sites or the company website but if you really want the scoop, you need to look at everything you can in the time you have available.