This is a perl-gtk program that displays a little digital clock. It's a lot like xclock's -brief option, but it allows you to specify your own format for the time. It also has a timezone function so you can see the time in other places. Here's a screenshot with two miniclocks running, one (blue) with the current time, and one (red) with the time in Switzerland.

miniclock requires gtk-perl and Date::Manip. Here is the source, and here is a sample rc file.