Here's the list of what I've got on the iPad. I have no experience how well they work on the iPhone though:
AeroWeather (brilliant for its simplicity. I particularly like that it only syncs when you hit the button, but then pulls in everything you need in one go. Saves a lot of cost when on an expensive 3G connection.)
iAIP (not all that good, but I paid two euros for it so I'm not getting rid of it. Before a flight, make sure to save the relevant pages locally.)
Flight Instruments (gimmick)
Air Nav Pro (very good although it does have its quirks)
WeatherProHD
iE6B
Furthermore my "aviation" page has bookmark icons for the METAR/TAF pages at OrbiFly and the NOTAM pages at metutil.appspot.com for my home base.