Noah Smith has a good article on the useful parts of economics, mostly microeconomics and its offshoots. He highlights specifically the usefulness of expertise in game theory, statistics, financial economics, and policy analysis based on microeconomic analysis.
As I am gearing up to teach an intermediate microeconomics course for the first time in several years, it caught my attention and I will be sharing it with my students before the first class. The article is at the link below:
http://theweek.com/article/index/255013/why-economics-gets-a-bad-rap
The curious incident of DD on the Web 