I use Google calendar. As with all Google apps it syncs across all devices, and is especially helpful if you also use gmail. Calendar is a default app on the N7. I'll schedule an appt. on the N7 calendar, for example, and have it send me a reminder via email, which I will receive on both my PC and N7. You can set reminders to arrive a day, half day, hours, and/or 10 minutes before the event.
Cheers,
- martyh