Researching a potential employer is not only important in crafting your resume and cover letter and for preparing for your interview - its also important for establishing whether or not the company is a good fit for you.
One of the great job search tips: there are many different resources for finding information about a company. Here are a few of the most reliable resources:
• The company's website (perhaps the most important resource)
• Hoover's Online
• Dun & Bradstreet
The wonderful thing about the internet is that you probably can do all the job search research from the comfort of your home. If not, your local library is a great resource!