This article details the most valuable Washington Quarters minted at the US mint and excludes rare error coins. It focuses on regularly minted coins, many of which are key dates. If errors are included they will be common errors that have been massed produced by the mint.
VG-8, or Very Good is a quarter that shows quite a bit of wear. Even though the obverse and reverse are worn, they still show strong design elements, although most surfaces do have a flat appearance. The obverse is weak although the letters are still clear and complete and aren't worn through to the edge. The reverse has pretty much a complete rim although most of the breast feathers and wreath leaves are indistinct. The wing feathers will be partially showing.
All quarters were 90% silver up until 1965 when the US Mint switched the blend to what many people call copper-nickel. The coin is now 91.67% Cu 8.33% Ni. Quarters listed on this page are of 90% silver content, meaning they contain .1808 oz of silver.
Of all American coinage, Washington quarters actually have very few key dates and very few errors. This means that, while any Washington quarter minted from 1932 through 1964 will have additional value due to the silver content, most quarters will hold a reasonably consistent value from year to year, from mint to mint.
With that said, there are a few standout key dates you'll want to be aware of.