One document that I now recommend everyone have is a HIPAA release. HIPAA is the Health Insurance Portability and Accountability Act. More information on the privacy aspects of HIPAA is available at privacy rights.org. The HIPAA release allows the person designated by the release access to your medical records. Usually, this is the same person that is designated as your agent in your medical power of attorney. The form I have seen also gives access to your medical records to other people designated in powers of attorney for financial affairs, trustees, etc.
Because HIPAA regulates the release of medical information, there is concern that unless specifically mentioned, medical records might not be open to your agent. A medical power of attorney should allow your appointee access, but there are always concerns about an overzealous privacy officer withholding access. So to be safe, if you are having end-of-life documents prepared by an attorney, ask that a HIPAA release be included.