Lights Off is the best game out for the iPhone. This is arguable of course, but overall I would say that it is just the best made game that I have seen so far. Hopefully some of the other games out there will get updates as the firmware updates and games get messed up. I haven't played too many games on the iPhone, but of the few that I have played, Lights Off is the best.
Lights Off is a very simple game where you try to make all of the lights go out. It seems like a simple task as well, but I have gotten quite frustrated with it at times. The fast reaction of the game is what makes it so good. When you tap the screen the game is very responsive.
I liked Labyrinth as well, but this game just seemed a lot more responsive.