Weather

http://www.nws.noaa.gov/om/marine
NOAA. Great source of weather information. Includes past weather map images of major storms.

http://fermi.jhuapl.edu/avhrr/
Excellent site by Johns Hopkins University. High resolution, near-realtime, color NOAA polar orbiting infrared satellite images covering the entire East Coast and Gulf of Mexico.

http://www.nmm.ac.uk
The official site of the National Maritime Museum in Greenwich, England. Interesting information about navigation. Great resource for historical information about navigation and life at sea.

http://www.mysound.uconn.edu/exrx_wx.html
Execution Rocks weather buoy information, tides, dew point, temperature, wind speed, radar and much more available.