The Cal, Sunrise and Google Calendar are good monthly planner applications available for both iOS and Android phones. All three are available for free in either the Apple or Google Play stores.
Cal features colorful photo backgrounds and a sleek, minimalist design. When the app is launched, it automatically jumps to the current day's agenda, showing all of events in a chronological list.
Sunrise also has a minimal, clutter-free look. The main view shows a list of upcoming events in an upcoming week with a minimized month view at the top. Sunrise categorizes events, paying attention to the keywords used in order to give each event a little icon. The Google Calendar app layout and design is similar to the Google Calendar program on a computer; information can be shared between a phone and computer on the same Google account.