Slashdot had a couple of articles on games that are coded in JavaScript in just a couple of lines of codes or even better in just a couple of characters of code.
I really like the way how coders go back to the roots and think about what you can do in just a handful of bytes. So here are two examples of games that are coded in just a handful of lines:
Tron (219 Bytes / project page)
Tetris (140 Bytes / project page)