There are dozens of weather apps for the iPhone, and most are variations on a theme. Not Rain Aware, an extremely interesting weather app that will tell you when it is going to rain, and when it is going to stop. It does it in very plain language, and as near as I can tell it does it pretty well.
The app figures out where you are, and after invoking some smart algorithms, it tells you about the weather not for your general area, but for where you are. It updates every minute, and also gives you a forecast for nearby points of interest, like airports, golf courses and sports stadiums.
This is a very different approach to weather, and a very personal one. I couldn't test the rain forecast as I am in the Arizona desert, but I looked at some other cities and even called a friend in Texas and asked him if it was raining at his location. It was, and I could clearly see that on the map, and told him when the rain would end. The app lists 1100 cities, and has a forecast, plus real-time radar so you can see what's coming, or going. The app will also give you information on sleet and snow.
My only negative is that the GUI is pretty ugly and cluttered. The developers are aware of this, and hopefully it will improve. The app sells for US $4.99, which is a bit higher than the run-of-the-mill weather app, but this app does a lot more, and behind it is a rather large server farm that spins up these custom forecasts.
I'm very impressed with the fresh thinking that went into Rain Aware, and if weather is really important to you, I suggest you take a look at the developer web site to learn about the science that is behind this app.