If you're a bit geeky, like myself, you may want to check out Binary Clock X in BlackBerry World. There are a few binary clock apps to be found but I quite like the way that Binary Clock X looks. One thing about it though is that it also includes an actual digital clock which is a bit of a let down but I guess it caters to all by doing this.
The app has an explanation of how to read the binary clock, again showing signs of catering to all users rather than hardcore geeks. You also have the option to set an alarm through the app though I haven't made use of this myself. If you like variety, then you can also change the colour of the LED of the binary clock.
What I would like to see is the ability to turn off the fact that it shows the time in digital form too. There are other app that show just the binary clock but I prefer the way this one looks visually. Binary Clock X is available from BlackBerry World and it is free. If it appeals to you go check it out now.