When I served in Botswana our primary focus was HIV/AIDS. We did not cure HIV during our service, and we didn't put much of a dent in the prevalence rate. Since HIV/AIDS work is such a tough primary project, most Peace Corps Volunteers in Botswana achieve the most personal satisfaction from their secondary projects.
I taught Information Technology skills to a lot of people. I had friends in several NGO's and I taught one-on-one with them. I also taught several workshops on Word and Excel in my office. The biggest part of my IT education was in the local library. I went twice a week and taught the library employees for an hour before they opened, and then taught the library customers for a few hours.
Teaching IT is fun and many of my students had to be taught from the most basic level. "This is a mouse. This is a monitor...." Many had never touched a computer before. Funny thing... no matter how little they knew about computers, when I asked what they wanted to learn they almost always said they wanted a Facebook account.
Remember that as an American who most likely grew up with a computer in your bedroom, your classroom and your office; you know a lot about computers -- even if you don't think that you do -- and you have a lot to offer. It is an easy project that most will appreciate. So if you are running a little low on ideas for a secondary project think about teaching IT.