Even in uncirculated condition, 1922 is such a common date for Peace dollars that the value is primarily for the silver content. As of 1 February 2013, it's worth just over $24.
The is no 1921S Peace dollar; Peace dollars were not produced in San Francisco ("S" mintmark) in 1921. If your 1921 dollar coin is a Peace dollar, it was produced in Philadelphia and has no mintmark; if it has an "S" mintmark, it is a Morgan dollar produced in San Francisco).
The 1923-S Peace dollar is very common, circulated coins are valued at $16.00-$24.00 depending on how much wear the coin has.
Peace dollars were made from 1921 to 1935. An 1879 silver dollar is called a Morgan dollar after its designer George T. Morgan. There's more information at the Related Question
what was the value of a dollar in the 1960's
Circulated coins are $25.00-$90.00 Mint State examples are $150.00 or more
Your 1928 eagle silver dollar is actually a 1928 PEACE dollar, the first Silver Eagle bullion coin was made in 1986. But for this year of issue Peace dollar it's very important to see if there is a mintmark (S) on the reverse just above the eagles tail it makes a big difference in value. If you see the S a low value for the coin is $16.00 no S low value is $250.00. Take it to a dealer or collector for an assessment
It should be valued at $15 - $30 depending on the condition of the coin.
No D's in1928,but the S runs from $35.00 to $65.00 in circulated grades
$14 (retail) in average circulated condition, up to about $30 if almost no wear is visible.
Morgan dollars were minted from 1878 to 1904 and in 1921. Please check the back of your coin. You have a Peace dollar rather than a Morgan.
The last Morgan dollars were dated 1921. Your coin would be a PEACE dollar. Please see the Related Question for details.
To date no 1928-S Peace dollar has been graded MS-69 by a major grading service, a few MS-66 coins have been certified but none higher. Value for the MS-66 coins is about $40,000.00