A number of excellent online services can help you find the best charities, or check out someone claiming to be one. You may find the following websites quite helpful:
Charity Navigator: Browse charities by state or city or by ratings; has several Top 10 lists and informative articles.
GuideStar: Another resource to check out a charity, searchable by state or city; you can also read or submit charity reviews.
CharityWatch (American Institute of Philanthropy): Allows you to search for top-rated charities by your issue of interest/cause; each charity is graded on the A-F scale.
GiveWell: A unique site that offers in-depth charity research, resulting in a VERY short list of recommendations for charities that meet their specific (and very rigid) criteria; their end goal is to determine which charities provide “maximum impact.” Very interesting and innovative company, which is a nonprofit itself.