Okay, this one's been a classic for over a 20th of a century.
http://www.adamatomic.com/canabalt/A simple, but addictive flash game. The object is to run as far as you can. The only control is a jump button.
The rules:
1) You must play the version at the url above.
2) You must not alter the function of the flash animation in any way.
3) If you have the highest score so far, post a screenshot to the thread. (ASAP, honor system)
For the person that runs the farthest that does not already have one by 1AM Eastern Daylight Time Tuesday night/Wednesday morning (you guessed it) I have a t-shirt:
If you already have one, play along just for fun.
Looks like the highest I ever capped was 14k: