What are rare dates for silver Washington quarters?

A number of early Washington quarters are considered to be moderately rare.

The key dates are 1932-D and 1932-S, with retail values in the range of several hundred dollars even in moderately worn condition.

Most other dates are not scarce in circulated condition, but a few are significant in AU or UNC, including Denver issues from 1934, 1935, and 1936.

There's a list of specific prices at the Related Link below.