March 2014 Update! Version 5.1 of the code is out with bug fixes and a nice lower case font. Get it while it's hot! The link is on the last page of this instructable!
This clock uses the classic video game Pong to tell the time. The 2 players automatically win and lose so their scores show the hours and minutes. It's not too hard to build and should cost less than $100. All the parts are easily available on eBay and the software code is free to download!
The clock can also show the time written in words such as "Ten Past Twelve", with large or small digits and with a slide or jumble effect. The date pops up every now and again too, printed out with a retro flashing cursor effect. A menu screen lets you choose the display mode, or you can have the clock pick a random mode every few hours.
The project uses 2 bright LED matrix panels from Sure Electronics. You can buy them in red or green with either 3mm or 5mm LEDs. An Arduino runs the main code and a DS1307 clock chip keeps time, even when the power is off.