Simple addon that chimes on the hour. You can configure the sound, whether to chime once or H times, and the time in mSec to wait between chimes if you have it set to chime the number of hours.
No GUI, /coth for commands.
To change the sound, get the path from, for example: http://www.wowinterface.com/download...dforWrath.html
and paste it into /coth sound, like:
/coth sound Sound\\Creature\\CThun\\CThunYourCourage.wav
(You can leave the quotes or make the \\ into \ if you want.)