Google Weather Feed
It’s the XML feed that Google uses to provide weather data. I’ve used Yahoo!’s weather feed before, but it’s not as complete. And The Weather Channel’s feed is more complex than I care to deal with. (It includes a developer kit!) Like Goldilocks said, Google’s seems just right. It includes the current conditions, four-day forecast, and even wind data.
The only downside is that you have to provide the city and state name. Supplying just a zip code would be much simpler. So, on a hunch a tried doing just that and it worked, too!
All that said, please remember that this feed is private to Google and not publicly endorsed (as far as I know). So use it sparingly if at all.