Popular Business Journals

Wall Street Journal (online 1979-present)
Harvard Business Review (online 1922-present)
Business Week (online 1975-present)

Top Scholarly Business Journals

These journals currently have the highest impact factors, according to Journal Citation Reports, 2007:

Journal of Marketing (online 1936-present)
Academy of Management Review (online 1976-present)
Marketing Science (online 1982-present)
Academy of Management Journal (online 1963-present)
Strategic Management Journal (online 1980-present)

Article Databases and Data Sources

ABI/Inform
This full-text database includes coverage of historical business, local and regional business journals, international scholarly business publications, and marketing information.  Searches can be limited to scholarly articles only.  The search interface is the same as ProQuest, so this might be a good choice if you are used to using that database.

Business Source Complete
This full-text database includes articles from popular business magazines, trade publications, and scholarly journals.  The basic search allows searching by industry and company as well as the more typical keyword, author, subject, and publication, and there are links to browse company and industry profiles, country reports, and market research reports.  Much of the financial data comes from Datamonitor.  

Alphabetical list of all Business databases.
You can also browse the database finder by subject to find databases for sub-topics within Business. 
Here's a 1-minute tutorial showing how.

Ford Library (at Duke's Fuqua School of Business) database lists.