Canabalt is a fun little Flash game made by AdamAtomic using his flixel library. In the game, you control a running man as he makes his 'daring escape', presumably from the futuristic robots that can be seen destroying the city in the background. All you have to do is press the X or C key at the right times to jump over obstacles and to leap to the next rooftop, which gets pretty challenging after a while. The audio and visuals are quite good and do a great job at creating a sense of urgency. Give it a try.