http://gabrielecirulli.github.io/2048/
Just found this addictive numbers game (if you're into that sort of thing).
Simply use the arrow keys to move all the tiles in that direction and when 2 of the same value collide they join to form one of double the value. The objective is to get to a tile with value of 2048.
My highest valued tile so far is 256 - can anyone do better?