It depends on what you want to do with your life, I think. But here are some good general ones:

• Group communications. As a software developer, you'll probably be working in groups for most of your career. Learning about how groups interact and how communication within groups occurs would be beneficial.
• Economics. I would recommend an engineering economy course that covers topics such as present worth and future worth analysis, rates of return, life cycle costs, project decisions, and so on. However, some kind of economy course should be taken, even if it's only microeconomics or macroeconomics.
• Organizational behavior. I took an OB course and it's very much an applied psychology and sociology course, taking psychological and sociological concepts and applying them to how organizations work.
• Technical writing or technical manual writing. Although any kind of writing course would be a good idea, technical writing would not only improve your writing skills, but also help you with the creation of technical documentation, something you might be doing at work.