Take a look at the popular BellTime, a freeware program obviously for Palm OS devices with recent fixes for the Centro. Highly customizable alarm clock for PDAs with Palm OS including Centro Treo TX and more.
In the Lite version you can fill 5 slots with:
An analog clock with flash alarm (4 slots)
A digital clock (2 slots)
Daily alarms
Weekly alarms
Single alarms
Timers
Stopwatches
Per city time zone bars
An info bar showing the next event
A bar for setting system time and date
An analog egg timer (4 slots)
Every alarm can trigger a circle pop up with variable snooze, the standard OS pop up, play sound only, or launch one of the applications on the device.
Midi sound with volume escalation and repeat.
For everything on the screen set your own colors.
Supports devices with PalmOS 5.0 till 5.4.9 and display resolutions 160x160, 320x320 and 320x480 (Portrait).