AeroWeather is the one I use a lot. It shows your selected METARS and TAFS fully decoded and readable - much quicker than logging on to the Met Office site, having to do a lot of finger work. It also shows whether the METAR is VFR, MVFR, IFR or whatever.
Be warned though - sync your iphone at the wrong time and you can loose all your apps. You can download them again if you remember the names (or look up your purchase history) but any data stored is lost forever. Sometimes you even have to pay again, other times the apps are no longer available.
I have PilotWhizz which would come in handy if I was not able to use my PC to plan my flights.