World Mints
The United States Mint
Almost every coin collector has probably purchased something from the U.S. Mint at one time or another. Keep abreast of all the latest news and releases about mint products such as the Presidential dollars or the next round of State/Territorial Quarters. Be sure to check out the Direct Ship program for Presidential dollars and help them to circulate.
The Bureau of Engraving and Printing
If it's paper money you collect, then you'll want to check out this website. The paper money counterpart to the U.S. Mint has lots of great information like how to detect counterfeit notes. Be sure to check out the Money Facts section and its list of topics on the right side of the page.
The Royal Canadian Mint
While producing over 1 billion circulating coins each year, the mint also produces special circulation coins to mark special events or occasions. The 2010 Vancouver Olympic mascot coins are examples of some of their most recent special circulation coins.
The Perth Mint - Australia
Founded in 1899, this mint was a branch mint of Britain's Royal Mint and was commissioned to produce gold sovereigns and half sovereigns which were used as circulating coins throughout the British empire. Today the mint focuses on bullion coins and bars for investment purposes.
The Royal Australian Mint
This mint was opened in 1965 and commissioned to produce Australia's decimal coinage beginning in 1966. Since 1969, the mint has produced coins for a number of other countries including New Zealand and Israel.
The Royal Mint - England
The official website of the Royal Mint. The amazing thing is that you can still get "original" proof sets from as far back as 1972.
Free Auction Archives
Heritage Auction Galleries
Of all the auction archives, Heritage is the king! If you have certified coins in your collection, then the Heritage archives are the best tool out there for keeping track of the market for your coins. The best part is the archives are free. But to view prices, you must first register with them (it's free too).
Teletrade
If it's certified lower grade rare coins or more modern U.S. coins that you collect, then Teletrade has the archives you want. While Heritage is king for rare coins, Teletrade takes the crown if it's an Eisenhower dollar or state quarter your interested in. Free registration opens up the full archives to you including prices realized.
Stack's
One nice thing about Stack's archives is that it doesn't take any registration to view the prices realized. Although I would rate Stack's archives second to Heritage for certified coins, they are clearly number one if you are interested in raw coins. They also put out some of the best auction catalogs that are better than most coin books and the top rate Numismatic Sun magazine. You can ask for a free trial subscription to the catalogs or a free sample copy of the Numismatic Sun.