Draw Something (free)
This game has really taken the app world by storm, mostly because it is tension-free and goal-free. You can play the game with contacts or let the app find an opponent for you anywhere in the world. Once you find a counterpart, you have to draw something for him/her to guess. You get points if the opponent is able to guess right. So the better you draw, the more points you win. The best part is the video view of how and at what stage the drawing was guessed.