I think weather pro is superb. It has estimated rainfall (quite often over estimated) radar, satellite and forecast. The met office iphone one which goes on the ipad is rather shit in comparison but it does have the warnings on it which can be quite useful.
I don't think the met office do a specific iPad app themselves, but you can use the iPhone one on an iPad, there should be a button to increase the size of the window.
I use the meteo group's WeatherPro app - I think it was originally recommended to me by OYBBK, Mumsnet's resident weather guru - and I've found it really easy to use, especially if you subscribe to the premium version, which is only £3.99 a year.
I have a met office app on my phone which I usually find quite reliable. However when I looked in the App Store for something similar for my new iPad [excited] I couldn't find anything produced by the met office. Can anyone recommend one? I would prefer to stick with the met office as I'm familiar with their format. Thanks.