Giving back to a world that has so richly blessed you is a noble goal. While your heirs might praise you for the thoughts, inwardly it might annoy some of them who might have been counting on some of that money or property to improve their lives and the lives of their families.
Life insurance is often the answer. Through a variety of vehicles (CRUTs, CRATs, gifts of appreciated property, etc.) gifts can be made and often the charity receiving the gifts will provide "Compensating Insurance" to replace the value of the gift at no charge to the family. You might even get an income tax deduction for the gift before you leave this world.
Robert has the answers.