It would be impossible to list all of the available career choices for someone with an MBA, but here are some highlights:

Wall Street

A number of people get MBAs specifically to go to work on "Wall Street" or banking. Of course, what we call "Wall Street" consists of many different things. There are applied mathematicians devising complex derivatives strategies, economists attempting to forecast the directions of interest and exchange rates, there are salespeople trying to sell securities to institutional investors, there are retail brokers who work directly with individual investors, there are specialists on the floor of the New York Stock Exchange, and there are analysts who use various models to try to predict the performance (and thus the value) of companies. And that's just a small list. Most of these jobs are either heavy in finance or in "relationship" building and networking. An MBA graduate will typically start out in some kind of analyst role, providing research for more senior bankers. The analysts work their asses off for a couple of years, and are then either promoted or shown the door. Once past that hurdle, the bonuses become large and the competition fierce.

Consulting

Again, this is a very broad term. Consulting firms are basically providing a service (based on their knowledge and techniques) to other companies. Consulting companies can be experts on information systems, compensation, management, strategy, operations, and a million other things. Consultants are on the road a lot, and work long hours. They start at a junior level, working on teams led by more experienced managing directors or partners. Many firms have a partnership structure, which means that making partner becomes the brass ring for anybody starting out. The most successful consultants are not only good at analyzing and problem-solving, but are exception builders of relationships, which allows them to mine their networks of contacts for extra business. Having a stint at one of the major consulting firms looks great on a resume, and can lead to upper-management opportunities at other companies down the road.

Industry By "Industry," we mean companies that make and sell stuff. This could mean a chemical company, a consumer-goods company, a software company, or a logging company. These companies typically need MBA grads for functions such as marketing, sales, product management, accounting, and functional management. You may have to move to some strange city in the Midwest, but if you're sharp, the road for a product manager to an executive position is well-travelled.

Academia Believe it or not, some MBA students become so interested in research that they decide to stay in school and go for their PhD. This may seem like a waste to some people, but if you get your PhD and an academic position, there are many opportunities to use your position to make money by consulting, writing academic texts, serving on company boards, and advising entrepreneurial students when they start their own ventures.

Obviously, there are many other options besides these. But this gives you pretty good flavor of what's available. No matter what type of career you pursue, expect long hours, hard work, and a lot of competition. In the end, it's probably better on an hourly basis than law or medicine.