*Travel photographer. You might do this for a company, freelance (or for yourself, perhaps creating a book to sell from your photography) or even for a travel agency.
*Wedding photographer. Obviously, you'd be photographing weddings -- this involves a lot of night and weekend work.
*Studio photographer. You might own your own studio or work in someone else's, but either way, you'd work mainly in portraits and group photos.
*Freelance photographer. You could end up doing just about everything -- from work for companies to birthday parties to fashion photography, based on whatever you can get a temporary job doing.
*Photography in journalism -- photographing for newspapers, magazines, etc.
*Photography for a certain company. This one varies based on the company itself, however, occasionally a company will require a full-time photographer.
*Fashion photography. This one isn't hard to figure out -- shots of models for clothing, makeup, hair.. pretty much everything. This is one form that can happen pretty much anywhere -- in and out of the studio.