Notificant

Notificant for Mac OS X sits quietly in the menu bar and displays new reminders at their scheduled time.

Creating a new notification is as simple as pressing a keyboard shortcut. The app features a minimal user interface and is very good at getting out of your way.
Create new reminders with the help of a global keyboard shortcut.
Send notifications to other Macs and iOS devices remotely.
Send scheduled notifications to yourself via e-mail.
Growl integration and non-intrusive custom notifications.
Nice unique and pleasant notification sounds.
Localized in French, German, and Japanese.