Tetris video game on television
http://www.web-ee.com/Schematics/PICTetris/PICTetris.htm
http://www.geocities.com/CapeCanaveral/Launchpad/3632/crono.htm
http://dt.prohosting.com/pic/pongschem.gif
measures your reaction time, and can be built on a breadboard.
http://www.nutchip.com/progetti/react_en.htm
circuit takes care of lighting the appropriate LED to indicate the winner
http://www.aaroncake.net/circuits/race.htm
At home like in TV shows. Complete with sound, lights, and response timer. Up to 3 players.
http://www.nutchip.com/progetti/quiz/quiz_en.htm
http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.html#ASCIISCHEM_002
A LED dice, bright, unbiased, and spectacular. The display uses 7 LEDs to simulate the faces of a real dice.
http://www.nutchip.com/progetti/dice_en.htm