There has been a massive growth in potentially relevant physical (sensor/IoT)- cyber (Web)- social data related to activities and operations of cities and citizens. As part of our participation in smart city projects, including the EU-funded CityPulse project, we have analyzed a large number of of use cases with inputs from city administrations and end users, and developed a few early applications. In this talk, I will present some exciting smart city applications possible today and venture to speculate on some future ones where Big Data technologies and semantic computing, including the use of domain knowledge, play a critical role.