INavX is really nice and it's companion tides app work together nicely. TnL (thunder & lightening) is an app to tell how far away the strike is (free) 'Sunrise & Fall is anothe free app that gives you both sun and moon times. There is another app called 'Phases' (again free) to give you moon phases. Intellicast for weather & Hi-Def Radar for squalls and storms.
There are many more but we like those. If you like exploring the skys you'll really like Star Walk. Point the Ipad at the sky and it shows you what's there as you pan the Ipad around.
'Intellicast' has a marine Intellicast app that is about $6.00. I may purchase it as it looks like it has a lot of useful information for boaters.
INavX, AyeTides, Sunrise and Fall, TnL, Phases, Intellicast, Hi-Def Radar, Star Walk. Get them all.