Statistics
 

Technically speaking, this is not a math class. It is however, one of the most applicable classes that are taught by most math departments. Students from so many different disciplines take this class in order to acquire the necessary statistical and the computational skills. Many find some of the topics to be very theoratical and difficult to grasp. At times, solutions to the problems rely more on reading and comprehension of the various case studies than any calculations. 

Graphing calculators such as TI 83/84 are extremelly useful in these classes. However, some teachers do not let students use them on the tests, so you should find out the class policy befor purchasing one.