I took a quick look this AM after my story yesterday about the NWS providing XML weather info and noticed that I don't seem to have made any comments here about Weather Underground. If you haven't been getting your weather here, you should be. The service is free (with a cheap fee if you want the ad-free version) and it provides extremely thorough information.
Although the views aren't as pretty looking (as in clean) as the competition (like weather.com), you get a lot more data and I believe also a lot more information.
To top it off, they have a nice mobile weather service, that contains a ton of information in a concise format which is particularly well suited for phone browsers and PDAs.
Check it out.