Here are links to some great resources:

Coin Collecting - Prices for foreign coins

Coin Shows - Check for upcoming coin shows

Coin Supply Express - coin supplies of all types

Commodity Research Bureau - Source for commodity research and prices
       
Credit Suisse - Bank custodian and vault for gold and silver

Fisch Instruments - precision instrument maker for the coin industry

GFMS Ltd. - World mine industry counsultant

Heritage Auctions - Reputable coin auction

KITCO - source for real time gold and silver market conditions and charts

Krause Publications - offers targeted world coin data and a very useful Gold Value Chart of the most common bullion coins

Numismatic Guaranty Corporation (NGC)

PCGS CoinFacts - an excellent Internet tool

Professional Coin Grading Service (PCGS)

Rutgers University - Risk quiz
      
Stacks - Reputable coin auction

Teletrade - Reputable coin auction
   
The Coin Dealer Newsletter
      
World Gold Council - membership is made up of gold mining firms

World Coin Gallery - the name says it all!