Chef de Cuisine
This is the apex, the chef whose initials are etched into the silver flatware, and embroidered onto the washroom towels. This chef has the vision, conceives the dishes, imbues the whole restaurant with his/her personality. This would be the person who appears on television. Sometimes, if need be, chefs de cuisine even cook.
This is a nebulous title, as only the biggest, most famous chefs de cuisine follow themselves with executive chefs. Executive chefs run the whole kitchen when the big boss isn't around and are often employed when a chef has more than one restaurant. They hire and fire the staff, determine costs, revamp the menu, take care of all administrative tasks, interact with the dining room managers, and generally oversee the well-being of the restaurant. In smaller, less flamboyant restaurants, the Chef de Cuisine sees to all this, and an executive chef would be redundant.
Next under the Chef de Cuisine or Executive Chef, depending on the restaurant, this chef is always in the kitchen. He/she comes up with the daily specials, takes inventory, watches over the staff, expedites (see Expediter, below), and basically does all the hands-on work. There are sous-chefs of two ilks: those who will soon move on to open their own restaurants, becoming Chefs de Cuisine, and those who will remain as they are, preferring the rhythmic rigors of the kitchen to the bright lights of chef stardom.
Generally the sous-chef, the expediter serves as the liaison between the customers in the dining room and the line cooks. He/she makes sure that the food gets to the wait staff in a timely fashion, so that everyone sitting at a particular table is served simultaneously. This job is all about coordination and timing.
The pastry chef is like the sous-chef, but reigns over the pastry section, which is usually tucked far away from the heat and bustle of the main kitchen (to protect delicate soufflés, fragile spun sugar, and temperamental chocolates). The pastry section has always been assigned less status than the main kitchen -- possibly because pastry was a traditionally female province (if there were any women in the kitchen at all, you might find them in the pastry section). Fortunately, this is changing.
The line cooks are the people who actually cook your food. They are divided up, either by cooking technique (saute, grill, etc.), or by type of food (fish, meat, etc.). When the expeditor shouts out an order (they always shout), the line cooks jump to prepare it. Most cooks work up through the line (working every position), before being promoted to sous-chef.
Chef de garde manger
The person in the garde manger section -- also known as the cold station -- plates all the dishes that do not require heat, such as salads, terrines, and sometimes desserts, if there is no assigned pastry person on the line.