NOAA's Office of Coastal Survey (charts & updates, coast pilots, etc) - http://chartmaker.ncd.noaa.gov/ 

NOAA's National Marine Weather Service - http://www.weather.gov/om/marine/atlantic.htm

Seven Seas Cruising Association - http://www.ssca.org/

Landfall Navigation (awesome site for gear) - http://www.landfallnavigation.com/index.html

Bluewater Books & Charts (great site for, you guessed it, books & charts) - http://www.bluewaterweb.com/

Discount Marine Electronic Wholesalers - http://marinewholesales.com/

Doug Ritter's Equipped to Survive Organization (Safety) - http://www.equipped.org/

Sea School (Training courses) - http://www.seaschool.com/

United States Power Squadron (regional & local clubs) - http://www.usps.org/newpublic1/guesthome.htm

Boat Trader Online (find your perfect boat) - http://www.boattraderonline.com/