The open-endedness - particularly, the customizability - of Android is exactly what makes me love it so much. And Make Your Clock Widget is a perfect example of that, offering seemingly infinite possibilities for what you can create. Don't believe me? Take a look at the sample screenshots:
Intrigued, I took a few minutes to play with it, and came away hugely impressed (note: I didn't include a picture of my final clock because... well, I made a goofy clock just playing around with the app.)
You can add the date and time in nearly any fashion or format you can think of - there are tons of options available.