Just about everywhere I went in Europe free maps were available at the train station or hostel. They weren't always the best but they sufficed. In Asia I relied more on my Lonely Planet book so I wouldn't worry too much about buying any maps there either. If you plan to visit more remote areas, good maps are available through Michelin, Kummerley & Frey; ITM & Hallwag, Lonely Planet (for city maps); and Nelles for select regions but it's prolly easiest to pick them up locally.