Political, Economic, Public Diplomacy, Management, and Consular.
The state department website has information about the different cones, but if you are seriously considering taking the test, I would recommend doing a little extra research and perhaps some informational interviews. The Hegemonist, a Foreign Service blogger, has also written about each of the cones--you can find the link here.
Because I am obsessed with culture and love working with people, I chose the Public Diplomacy track. Public Diplomacy (PD) is like Public Relations for America, and officers who work in this cone get to do a wide variety of tasks from working with the press to organizing cultural exchanges and attending cultural events. PD is also beginning to take advantage of new technology like twitter, blogging, and second life--a development that I find fascinating. I believe strongly that the arts and the public sphere are strong forces that bring people together and facilitate mutual understanding.
If you have time, check out the USC Center on Public Diplomacy wiki about PD and an informational video found on the CB3 communications blog.
If you want to know more about Public Diplomacy and New Technology, watch this TED lecture by new media guru Clay Shirky.