Most software clocks take up too much screen real estate or force you to fiddle with (or at least look at) the taskbar, which may be hidden.
TitleTime conveniently shows the time and/or date on the title bar of the active application and lets you set up to three alarms that can display a message and picture, launch programs or batch files and/or play a sound.
You get all this and more for free. However, TitleTime does not work with the title bars of Explorer or Internet Explorer.
The brainchild of Roger Sondermann, it is available at http://www.neuss.netsurf.de/~sonderma/titime.html