This is exactly the app i've been looking for and its very similar to an app i used on my WinMo called Re-remind. A few features from re-remind that I liked were:

Ability to change the notification tone (i prefer a distinct beep only).
Ability to change the volume (like i said, distinct beep)
Disable at certain times of day
Also notify on missed calendar events

I hope you can add these on the next version.