I use PilotWiz on iPhone (
Welcome to Pilot Wizz) and it's pretty good. You can store routes in it and retrieve them later, put in the wind and it generates your plog. Also does graphical W&B and will let you store envelopes for different aircraft.
It's free.
Only slight annoyance is that you can't put in 2 different wind values for legs of a route, so you get it to generate the route twice with different wind values. Also transcribing from the onscreen plog to written on knee plog is a pain (wish I could just print it out). Overall though, an excellent piece of software.