Air Nav Pro
Downloaded Air Nav Pro on my i phone 4 today, fantastic, what I liked is that you can place the i phone on your chart (mine has a incase cover which stops it moving around) and follow your track line whilst using the app to verify your Track, Altitude, Ground Speed etc.
I havn't downloaded the 1.5 charts yet as the free Open Street Map is brilliant with the Airspace showing layered over it, not quite as quick as the Garmin Skymap but if your going somewhere and you use a chart with your track plotted on it together with a Skymap and then your i phone with this app loaded it would almost be imposible to get lost. It is most probably great on an i pad, but would be to big to place the i pad on your chart.
Only problem is that it chews your battery so take your power lead !