The Internet makes buying gold online simple. Below are my favorite online stores for buying coins. These are banner ads. I will get paid a commission if you click through the link and make a purchase.
Golden Eagle coins is a reputable coin dealer from Laurel, Md. The site offers precious metal and collectable coins with an enviable collection coins of graded and bullion coins. As I am interested in the precious metal, I am partial to the bulk backs of coins.
I actually do most of my buying and selling of coins through ebay. There are enough coin buyers on eBay that you can run no-reserve auctions starting at a penny and usually get at or just above the melt value for lower grade coins. It is a great place to buy coins.
GoldSilver.com offer investment grade precious metals along with the resources to help you make the decision on when to buy and sell.
World Reserve Currency promotes coins as an alternative currency.
See links alive for more online coin shops.