Everybody from the age of 24 and down has had a Gameboy or a equivalent of the hand-held console when he/she was younger. There might be a little less people that actually wanted to build there own and even did so. Throwing together a Arduino Duemilanove, TouchShield Slide, DoubleWide,MeCap Lithium Backpack and a InputShield you can make a functional yet slightly smaller Gameboy your own.
The next example is a project made by Riley Harmon. He build an installation from custom electronics based on a Atmega8/168 micro-controller connected to a PC running a dedicated Counter-strike (First Person Shooter) server. When a player dies on that server one of the 9 medical bags of fake blood get a signal to release a little bit of blood. The fluid then slowly drips along the wall to the floor creating a bit of an alarming effect.
An project called Cassius How gives you the opportunity to use your fists as a brush. By punching against a pressure sensor filled punching bag, you can draw out a virtual 3d-animation. When you punch it the sensors relay their data tot an Arduino board that sends the data received over to a computer. The computer is running a software program that sketches out the different amounts of pressure applied to the punching bag in an OpenGL program.