• Academy of Management
• American Business Women's Association
• American Management Association (AMA): Be sure to take a look at the articles and white papers.
• Association for Financial Professionals: Continuing professional education, CTP exam prep, and career resources.
• Financial Management Association: Offers free membership for undergrads and MBA students.
• International Association for Human Resources Information Management, Inc.
• National Association for the Self-Employed
• Society for Human Resource Management (SHRM)

• Better Management / Knowledge Exchange: Search and browse articles on management-related areas.
• Free Management Library: Search a variety of management topics.
• Thinkers 50: A lot of the top 50 management thought leaders.  This site also includes videos.

Harvard Business School has some examples online of organizational culture.