ClockDummy!

ClockDummy is a great atomic clock that has the ability of telling the time with a nice voice and also enhance your system tray clock.

You can add a background image or simply a solid color, change the text color, font and style, enable atomic clock synchronization, enable clock seconds, 24-hour format, month, and day, or you can even set the program to use a new clock each time on startup. What is great and not commonly found in other programs is the ability to speak the time every hour, half an hour, fifteen minutes, or 12 hours. You can also add sound effects. The clock also enables you to add events so that you never forget them, allowing you to run a program or music, speak the time, play sound effect, display event message, or shutdown your computer. The clock can be absolutely controlled from the system tray menu and it is very easy to use.
In short, ClockDummy is a nice system tray clock enhancer, which offers many other options that you won't easily find in other clocks and which make it worthwhile.