Useful Links 

USCG - US Coast Guard
USCGBS - US Coast Guard Boating Safety
USCGA - US Coast Guard Auxiliary
USPS - United States Power Squadrons
AW - AccuWeather
ITC - Intellicast (weather forecasts by city)
AMTECH - Association of Marine Technicians
BS - Boating Safety - Boater's Resource Center 
NFPA - The National Fire Protection Association 
ABYC - American Boat and Yacht Council
ABBRA - American Boat Builders & Repairers Association
ASA - American Society of Appraisers
ASNE - American Society of Naval Engineers
BOAT/US - Technical Information Exchange
NMMA - National Marine Manufacturers Association - USA
NPGA - National Propane Gas Association

Magazines/Publications

American Marine Publishing's Powerboat Guide
Boating Industry From The Publishers of "BOATING Magazine"
Claims Magazine|
Powerboat Reports.com
Practical Sailor.com
Professional BoatBuilder
Boat & Harbors
Insurance Journal
Proceedings - USCG Journal
The Waterways Journal
Yachting & Boating World 

Digital Boat Brochures - Have an old brochure Emailed
Don Robertson's Marine Marketplace - Links to Every Boat & Engine Builder on the Planet. Well.... almost.
Engine Serial Number Locations & Model Year Data
Engine Serial Number (MerCruiser) & Model Year Data
Manufacturers Identification Code (MIC) Database - from the US Coast Guard
USCG Notices of Vessel recalls & Safety Defects

Boat Values

BUCValu - Used Boat Price Guides
NADA Guides - On-Line

Dictionary/Thesaurus/Encyclopedia

AskOxford.com - Oxford Dictionaries
Dictionary.com
marineterms.com/ - Practical Shipping Vocabulary
Maritime Dictionary - by m-i-link.com
Merriam-Webster Online
Online Nautical Dictionaries
TechDictionary - Thousands of Technology Terms
TheFreeDictionary - by Farlex
Thesaurus
Wikipedia - The Free Encyclopedia That Anyone Can Edit.

ASTA - American Sail Training Association
IMCI - International Marine Certification Institute - European Union Regulations
Lloyd's Register of Shipping
United States Electronic Code of Federal Regulations - Searchable CFR's
United States Coast Guard - Office of Boating Safety
United States Coast Guard - Backyard Boatbuilder's Handbook
United States Department of Transportation’s Maritime Administration (MARAD)
United States National Vessel Documentation Center
Look Up US Documented Vessels By Name or Number