I don't really do any flight planning, as I don't actually fly properly all that much! I am also limited by using the RXP GPS, since you can't load FSX flight plans into it. All that said, I have looked at (and liked) Flight Sim Commander (which is currently on sale at 30% discount from Just Flight until tomorrow). It's a bit confusing as it has all sorts of other stuff besides flight planning, but you don't have to use that. When I tried the demo I was hoping the 'black box' function would make the Twin Otter's flight data recorder more sophisticated, as at's based on the FS Commander one, but it didn't! Here's a good video demo of FSC.