Charity Village® This website, "Canada's super site for the nonprofit sector," includes plenty of general information about nonprofits.
The Foundation Center brings you "Knowledge to Build On." This organization publishes a multitude of resources & directories, maintains a network of nonprofit resource centers, and provides a rich site containing articles and foundation information including a search screen.
The Idealist website offers a list of useful websites for nonprofit information.
National Center for Charitable Statistics: Nonprofit FAQ page has a table with over 100 topics arranged in 5 major categories - organization, management, regulation, resources, and development.
The Internet Public Library has an impressive list of web resources for nonprofits.
Michigan State University Libraries offers an extensive collection of internet resources including a list of newsletters (with some region-specific information).