I am using PocketFMS for preliminary flight planning. It's an amazing
piece of software, especially since it doubles as a VFR GPS solution.
However, it is being produced in the Netherlands and while their
European data appears to be very reliable, the US mapping has some
glitches. For example airports are stored twice (e.g. LAX and KLAX),
weather info is not always updated and it's hard to find out whether
you did indeed get current weather. Also the Navlog printing may or may
not work. I'd recommend using PocketFMS to quickly plan your route,
then print it out and finish it by hand or using other software to add
wind correction.

I have also tried out aeroplanner.com and found it passable. My main
complaint is that it's entirely web-based and their server is not very
responsive. Planning a flight from scratch just takes too long.