If you're looking for ideas to make an app, the best ones come from necessity. What every day problems do you want them to fix. The best quality apps come those who had a personal interest in fixing the problem.
Well, since you baited me in then I guess I'd say that most problems have been touched already and all thats left is to improve on it. Better scheduling, better maps, more geofencing (pending bigger batteries), better options in media consumption etc/