Besides the possibility to work as a teacher in high school or as an academic researcher a degree in mathematics opens up a huge variety of possible career options. Studying mathematics is one of the best possible ways to learn analytic and problem solving skills. Mathematical methods lead to many interesting applications, for example in image processing, telecommunication or financial mathematics. A comprehensive overview with many concrete application examples of mathematical methods has been compiled by the Applied Mathematics / Numerical Analysis working group at the University of Wuppertal in the free publication "Erfolgsformeln" (German only).
For these reasons studying mathematics prepares you for a lot of career options. Mathematicians are working at banks and insurance companies, in software development, in consulting or at research departments. More information can be found e.g. on the web page of the American Mathematical Society (AMS).