I would pick topics that are current and have a strong opposition on both sides. Here are some examples.
Political
1. Arab-Israeli Conflict/ Israeli-Palestinian Conflict
2. Gay Marriage
3. The Supreme Court's lift on political donations
4. Gun Control
5. Legalization of marijuana
6. Public option for health care
7. The death penalty
These are all pretty common topics that you can find a huge amount of info on. Aside from #1 I wouldn't be surprised if a lot of your fellow classmates will choose these topics. As you didn't give much background info I'm not sure if that is a good thing. Hope I could help.