Google Calendar works great on the iPad and can be linked to the calendar app that the iPad comes with. You can color code your meetings, organize your invites, and set reminders.
Key Features:
View your calendar by day, week, or month
Organize all of your shared calendars
Change how you start your week and the time zone
Allow for background illustrations
Add events, reminders, and goals
Edit events, add important notes, and organize reminders