Calgary Coin Gallery : Robert Kokotailo is the owner of this shop that carries virtually everything and is extremely knowledgable about coins. He has helped me identify several "mystery" coins. For you Americans, remember that due to a favorable exchange rate, everything on his site is discounted at least 25%, perhaps more.
Robert G. Lilly: Robert has quite a selection of Ancient and Medieval coins at reasonable prices.
Jean Elsen: This site has the largest selection of Medieval coins for sale on the net. They are located in Belgium and are very helpful and knowledgable. They are always willing to help you with attribution or other questions you might have about ancient or medieval coins.
Guy Clark: Guy also has a good selection of Ancient and Medieval coins on his site.
EBAY Auction: This auction site always has a good selection of coins, as well as anything else you can imagine.
CGB : Michel Prieur operates this site which rivals Jean Elsen as the largest site on the web with medieval coins. I'm not about to count them all - I'll let you decide. Michel is very helpful and will answer almost any question you may have. This site is in France.
Check out one of my other interests at Jim's Gaming Page