2004 State Quarter Silver Proof Set. This five-coin "short set" issued by the U.S. Mint contains 90% silver quarters and had a production of only about half of the year's clad proof sets. The commemorative state quarters issued for 2004 were struck by the San Francisco Mint and pay tribute to Michigan, Florida, Texas, Iowa and Wisconsin.
2006 State Quarter Proof Set. This 2006 silver quarter set's mintage of 531,000 was just over a quarter of the production of the regular proof set that year. Included are 90% silver proof tributes to Nevada, Nebraska, Colorado, North Dakota and South Dakota featuring crisp, double-struck engravings and dazzling mirror backgrounds.