Yahoo Weather (free) has been my favorite quick-look weather app since it came out a year ago. I believe it looks better than Apple's weather app and provides more information.
Yahoo has posted an updated version, with some worthwhile features. You now get chances of precipitation in the 5- and 10-day forecasts. Wind chill information appears when it is relevant, and there are new animations for moon phases. Another new feature lets you swipe down on the photo to replace it with a new one. It's a small touch, but a nice one.