Which state quarters are valuable?

Certain state quarters can be valuable, particularly those that are rare or have mint errors. For example, the 1999 Delaware quarter with the "spitting horse" error and the 2004 Wisconsin quarter featuring the "extra leaf" are highly sought after by collectors. Additionally, quarters from the 1932-1964 era, especially those in uncirculated condition or from specific mints, can also command higher prices. Always check recent market trends and grading to assess value accurately.