Education, General Reference
The Bogleheads Forum is in a class by itself.
Any financial topic worth discussing is probably being discussed there, with intelligence and civility.
Also see the Bogleheads Wiki for investing articles.
Business and Financial News
Sites to Research Mutual Funds and Stocks
Gurus and Iconoclasts
The Economist - International business and economics.
Personal finance and investing, and commentary on business, economics and politics.
HBS Working Knowledge -
High-powered articles from Harvard Business School.
Personal finance articles.
Articles and lots of very clever interactive gadgets.
You can find lots of basic educational material and helpful links at two nonprofit sites,
The American Association of Individual Investors and
The Alliance for Investor Education.
Securities and Exchange Commission
Many More Links
Wachowicz's Web World is a huge list of finance links.