NAVIGATION - Garmin BlueChart Mobile is a free download then you purchase maps of N America for $35-$45. App incorporates ActiveCaptain data and overlays the info on the charts. Absolutely the best money you can spend for a great trip planner (iPad) or back up navigation system (iPhone & iPad). Check out vivideo at http://www.youtube.com/watch?v=bmtuk7Kyq4A
WEATHER - Intellicast Boating is the first of a kind weather app to incorporate marine weather info on satellite imagery or NOAA navigational charts. Use with an iPad 2 with GPS and location service is builtin. Cost is minimal for such a useful weather tool. Great for coastal cruising. Check out at http://www.intellicast.com/IntellicastBoating/
I have both apps on my iPhone and iPad. Garmin BlueChart Mobile is a one time charge and maps will download on both devices. Intellicast Boating costs for both iPad and iPhone.