Featured Sites:
Nonprofit Related

Nonprofit Databases and Listings

Guidestar
A web database of all IRS-registered charitable nonprofits includes 990 forms from IRS-registered charitable nonprofits

Urban Institute
Home of the National Center for Charitable Statistics

Maryland Secretary of State
Provides a variety of nonprofit links and resources as well as links to other state listings. 

Gale Group
Information on the 450,000+ membership associations

Better Business Bureau - Wise Giving Alliance
Ratings of nonprofit organizations

The Johns Hopkins Third Sector Project
Links to the Center for Civil Society, the Comparative Nonprofit Sector Project, and the Nonprofit Employment bulletins. 

Saguaro Seminar
Major survey on civic engagement in the US in collaboration with Robert Putnam

American Religion Data Archive
Links to major data sources on religion