iWeathr
iWeathr is the best radar app for the iPhone that I have found so far. Navigate to iweathr.com and locate your nearest radar location. Note that you won’t be entering the city where you live but rather the location of a radar installation. For help finding the nearest one to you go here. This implementation allows both rotation and zooming in – very nice!
Another nifty weather iPhone web application can be found at http://iphone.my-cast.com/ It’s a basic forecasting web-app but all that more powerful and simple.
*Update: kurt mentioned below that he prefers i.wund.com for it’s simplicity and the mass information that is displayed on the iPhone screen for that particular location. I have to say that it definitely does show great information, but the moving map on iweathr.com is the basic one that is hosted by the government’s weather website: http://adds.aviationweather.gov/radar/ which is the one that prefer using when scoping out the weather prior to flying. Thanks for the comments!

{ 2 comments… read them below or add one }
This web app is da bomb! This makes it unreasonable to get a specific downloadable pay app, because you still need to be connected to the internet to get latest internet radar feeds. Its now on my ‘front page’ applications (took YouTube off)! Thanks for the link.
-Matt
Not to bad, pretty clean. I’ve been using http://i.und.com and still like it better.