Numismatic Links:
Reference, attribution & valuation site for ancient Greek, Roman and Byzantine coins

American Numismatic Association

American Numismatic Society

History of Money in America

The US Mint

CoinFlation  find out the value of the base metals in your coins based on the current metals price

Coin Fraud - information on fraud and scams.

Coin Wiki

Beginner's Coin Collecting Guide

Coin Grading Services:
PCGS - Professional Coin Grading Service
ICG - Independent Coin Grading Company
NGC - Numismatic Guaranty Corporation of America

Online Auctions / Coin Dealers:

USA CoinBook


Heritage Auction Galleries

Coin auction site with links to ancient coin database listing auction results

Ancient coin auctions, there are links to big name companies like CNG & H Berk and smaller ones like Pegasi & Nilus

Auctions of US, world and ancient coins and books

Ancient coin shops and auctions

MA-SHOPS has a large selection of ancient to modern, world coins. The shops (dealers) have coins for sale and auctions

Several companies auctions of US, world and ancient coins

Other Coin Clubs:
Bellaire Coin Club
Greater Houston Coin Club

Coin Connoisseur
Coin Today

Coin Shows:
Coin Shows

The National Numismatic Collection at the Smithsonian Institution
The Museum of Biblical Coins

Other Useful Links:
Texas Metal Detecting Clubs