Harvard Business Review
Requires paid subscription. The pre-eminent business magazine, with frequent articles on strategy. Where leading academic research on management is first shared.

McKinsey Quarterly
Requires paid subscription. The latest thinking from the largest Management Consulting company in the world. Frequent articles on strategy.

Boston Consulting Group
Free. Subscribe to their publications, and get new ideas from their "Strategy Galleries". BCG have been at the fore-front of strategic thinking for many decades.

Jim Collins
Free. Audio clips, articles, bibliography, toolkits and thought provoking material from the strategy guru who wrote "Good-to-Great".

Strategic Thinking Group
Free. Download strategy maps and get ideas from the site.

The CEO Refresher
Free. Independent thinkers submit articles, with frequent ones on strategy.

MIT Sloan Management Review
Free. Subcribe to the magazine from the Sloan School of business.

12manage
Free. Comprehensive management knowledge-base with good coverage of strategy and excellent coverage of other management topics.

Corporate Executive Board
High annual membership fee. Unique value proposition, but for large companies only. Members have unlimited access their knowledge-base of best practice and network of thousands of companies.

CIA - The World Factbook
Free. First point of call for information about any country.

Google
Free. Whatever the topic, try it! You may hit pay-dirt!