Cost: Free 4th Grade, 5th Grade, 6th Grade, 7th Grade, 8th Grade, High School
Yasp! is a student planner app for Android that is free and has some great features. It's easy to use and set up your class schedule, as well as enter assignments and due dates. In landscape mode, it displays a week view and can support two week schedules (A and B weeks like my school uses). It supports recurring events, class schedules, assignments with reminders, and one time events like exams.
It does not sync to any desktop version, but is very simple and easy to use and will be a great resource for many students.