SkyDemon on the iPad is really good. I used AirNavPro first, but I like SkyDemon much better.
AeroWeather for decoded METARS and TAFs is very good, although you can get same info through SkyDemon as well, once you have created a route.
On the recommendation of others on here, I've started using LogTenPro as a back-up to my hard-copy log book, and I am happy with the choice.
Not specificly for flying, be sure to get GoodReader.
Finally, get a good anti-glare screen protector. My research took me to MagicScreen (on Amazon) and it's very good. They do various ones - it's the anti-glare one you need.
I'm tempted by iPlates for the sheer convenience but haven't tried that yet.