MonkeyClock

The MonkeyClock AddOn for WoW displays the time in a nice customizable frame.
The clock doesn’t use many resources. You can configure it in the Interface Options.

MonkeyClock Features:
AM/PM or 24h format display
Alarm notification and Snooze feature
Color + opacity of frame customizable
Color + opacity of border customizable
Frame is movable, resize-able and lockable
Right-click opens options (can be disabled)