Not as everyone believes
ALL silver dollars DO NOT have 1 troy ounce of silver in them.
In fact the only common US one that is minted, at one ounce is the Silver Eagle.
The others are around ¾ ounce mint weight.
Link to PaysonDeals on Ebay with Silver Eagle's
Click on these links for more informantion
For the silver eagle specifications and informantion:
Information link on US coin fraud issues
Silver changing Prices