GuideStar --This is the free version of this database. The Business Library (BIC) has a subscription to GuideStar Premier which gives more detailed information. It must be used in BIC. Ask at the desk.
Charity Navigator --Allows searching by charity name. Gives rating, programs, history, 990 Form, and comments.
Give Well--Covers limited charities. Gives very basic information.
Better Business Bureau for Charities and Donors--BBB evaluates charities and gives a fair amount of information on them.
IRS Select Check Tool (Organizations that filed 990's)--Has rules for exempt organizations and filing information. It also has news about specific nonprofits.