The Jeppsen Plan2Nav saved my bacon a couple times when my old Garmin gave me the "blue screen of death" Not fun using a phone as a chart plotter, but it works.

For internet connection PDA Net http://pdanet.co/ This replaces the phone company's "air card" or modem with your phone. One less thing to buy and have to have an separate line charge for. It also lets you set up your own hotspot at no extra charge. Right now it is less than $10 one time fee. It is as good as most WiFi if you have 4G, not bad on 3G and very slow with 1X. We have used it from Maine through Florida. The one caution is you need a healthy data allowance since it tends to get heavily used.

Apps Work well with 3G or better
Radar Now finds nearest NWS radar site and runs a series of scans and forecast Free
Marine Traffic Shows big ship positions near you by MarineTraffic.com Free Sometime good, other times bad due to holes in their land reporting stations.
NOAA Weather by Pandamonium Free Shown the NOAA Spot Forecast and can locate itself.
Marine Weather by Bluefin NWS Marine forecasts nationwide Free
Weather Bug Free, self locates, has forecast, radar and lightning

Plan2Nav by Jeppsen Free but ~$30 for the East Coast and Bahamas Does not require internet once installed Does link/display Active Captain
Currents Tidal Current prediction by Fly2Map Free Does not require internet once installed

Web Based
NOAA 7 day Change to your home before saving
http://forecast.weather.gov/MapClick.php?CityName=Edgewater&state=MD&site=LWX&textField1=38.9091&textField2=-76.5477
Weather underground Marine
http://www.wunderground.com/MAR/AN/532.html
NOAA Tropical
http://www.nhc.noaa.gov/gtwo_atl.shtml
Salty Southeast Cruiser’s Net
http://cruisersnet.net/ Best trouble spot reporting site – more accurate and timely than Active Captain, but only for below the Virginia line