If you're planning about taking a 2nd course. It's always a good practice to look at where you are right now (in terms of career) and where do you plan to be in the near future? Always consider your plans for any trainings and your further studies. There's not much use of spending a lot of money on something that you won't be able to use right away.
But here's my recommendations for cross-functional or generalized courses :
(Management) Accounting
Mathematics
Business Administration
Advertising Arts
Information Technology
Economics
Psychology
Industrial Engineering
Law