In the Middle Ages, great nobles ate the most formal dinner, around noon or one p.m. Their dinner was more than a meal; it was an ostentatious display, a statement of wealth and power, with dozens of servants attending in a ritualized performance. Cooking for this grand, daily show began hours in advance, and the preparations for presentation began at 10 or 11 a.m. The meal might take hours, and be eaten in the most formal and elaborately decorated chambers. Lesser nobles, knights and manor holders ate a far less formal dinner, but at the same time of day.
Middle-class tradesmen and merchants, however, had to eat a little later. Their day was bounded by work, not by feudal rituals. They couldn't leave their shops to see to their own dinners until clients and customers had gone off to their own. So merchants and traders would eat at one or two in the afternoon, and then hurry back to meet the afternoon customers. The middle-class dinner might be served by one or two servants and consisted of bread, soups, pies, and perhaps meats and fish. The dishes varied with the season, and from country to country.
Peasants broke off after six or seven hours of work in the morning to have dinner around noon. This was their main meal too, consisting of bread or porridge, peas or beans, perhaps with some cabbage, turnip or onions thrown in. Sometimes they had meat, fish, cheese or whey (a byproduct of cheese-making). Their meal was much like that of the middle class except there was usually less to eat, and little variety. They ate far more at dinner than at breakfast or supper.
Also, there's a sample magazine (pdf) that has articles on Eleanor of Aquitaine, Thomas Becket, Frederick Barbarossa, the 3rd crusade, and William Marshal (the "greatest knight who ever lived"). http://www.history-magazine.com/HM_Sample.pdf