If you are looking for a simple yet elegant game that you cannot put down, look no further than iWire by Origin8.
In iWire, you tilt your iPhone left and right to keep a ring from slicing through the twisting and turning wire. It sounds pretty simple, but it actually becomes pretty hard very quickly. The game features three difficulty modes: easy, medium, and hard. However, medium and hard both need to be unlocked by beating the difficulty mode below it.