So you want to be a nonprofit professional?
Well so did I! And let me share with you this invaluable tool from Idealist.org (a project of Actions without Borders) that I used for more than my professional search for a career in nonprofits. In addition to a career search, it also helps you develop a sense of your strengths, mission purpose, and a refined look into your skill set before you even apply for one job!
The book is called the Idealist Guide to Nonprofit Careers for First-time Job Seekers. It can be found here and in your local bookstores.
I recommend to start reading it immediately. Not all chapters will be useful if you are looking for a position, but some will be useful for those already employed. My personal favorites are the chapters in the beginning, as they promote the focusing of your tasks mentally early on in what you desire in a nonprofit career.