SmartMoney: The Internet version of this excellent publication features a lot of good reading material plus some useful tools, such as the Portfolio Tracker. SmartMoney is a joint venture between Dow Jones & Co. and Hearst SM Partnership.
Morningstar: A definite resource, specialized in fund investing. Morningstar provides extensive data, fund and company analysis, commentary, portfolio tools and other surprinsingly good features, such as the Investing Classroom. They also publish several books and guides.
ETF Connect: Essential data for researching about individual exchange-traded-funds. Easily browsable, up-to-the-point information on exchange-traded funds (ETFs), closed-end funds (CEFs) and exchange-traded notes (ETNs), which are all collective instruments that are traded in stock markets, as if they were ordinary stock.
Yahoo! Finance: Loads of information, actual and historical, ready to chart. Includes detailed info about individual stock and funds, such as modern-portolio-theory (MPT) statistics, analysts' opinion summaries, insider transactions, comparisons with competitors and forums.
Google Finance: Another information-rich site like Yahoo! Finance. Info is not as plentiful but charting features are stronger. Google also offers Google News for searching for the latest news about our topics of interest.
Investopedia.com: Excellent encyclopedic resource about investments. "Must" visit when in need of a precise definition for an investment term. It also provides various tutorials, tools and community features.
BioMedReports: Information, commentary and other resources about the global healthcare sector.
Investor & Trader: Airelon's blog, where he comments, with an informal and entertaining style, his views on the economy and ideas for investing and trading, judiciously stressing the distinction between these two. His posts are frequently in the form of videos.