More on
oysters- there are other subspecies not mentioned by sneff above in his otherwise informative piece.
One is the atlantic oyster, Crassostrea Virginicus, which is the most common one eaten in the US, also the lowest priced generally. They grow all the way down the east coast and into the Gulf of Florida. The harvests are getting smaller every year, most notably in the Chesapeake Bay, but they are still very common and well known. The Blue Point Oyster is a well-known example, with around 35 million grown a years. I personally think they are less attractive than Gigas and also have the problem of usually being grown in water that has too many man-made influences on the taste
The Olympic Oyster is native to the west coast of the US from Oregon to Alaska and has a small niche market as a varietal, but they are smaller and have a very mild taste.
One other variety that has a strong place in the gourmet market is the Kumamoto, named after the bay in Japan where it was first taken from (and from where it is now extinct- it exists only as a farmed species). This is again a milder taster tasting oyster, but sweetly creamy and worth a try, as they all are.
Advice on finding a really good oyster- anybody selling oysters should have the interstate shipping tag with the date of harvest on it. Look for under 10 days, and if the oysters have been properly chilled they should taste fairly represtative of what they where just out of the water. When you eat an oyster, remember that the taste is a reflection of the water where it was grown- if you taste chemical overtones, there may be a pulp mill in the watershed, if you taste pavement, you are probably eating a Blue Point (from Long Island Sound). The best tasting oysters come from isolated watersheds in the West Coast, especially Alaska, or from the east coast of Canada. When you eat a really good oyster, you don't need to put any enhancers on it to make it taste great.