The American Association of Colleges of Nursing and the National League for Nursing Accrediting Commission are both national organizations which accredit graduate programs in nursing. Their web sites provide information re: choosing an appropriate graduate program.
Brainstorming with fellow nurses who already have graduate degrees or who are attending graduate school is a great way to learn more about the opportunities available in graduate school. You can search online for individual programs near where you live or in areas where you would like to live. You can also contact faculty from your undergraduate program for information and advice re: graduate programs and graduate study in general.
Prior to sending out applications (which costs you time and money), it is a good idea to visit potential programs to meet their faculty and graduate students, and to get a sense of 'fit' for your specific interests and needs.