Jesus taught a number of times about being a good steward. Sometimes stroking a check to a ministry or charity may not be such a good decision. It all depends on what the organization does with the money. Will the funds be used wisely or not?
I recently came across the following page that provides a bunch of resources to help you check up on what a ministry is doing. It is best to support those organizations that you personally have a connection with. And it always makes sense to do a little homework before adopting a new one.
Of course, prayer is the first check that any Christian should do before any giving at all. For the Christian, charity begins as an act of worship to God. While man is the recipient of the aid, God should get the glory.
May these resources help you.
Organic Faith - Searching for intimacy with God in a postmodern world 