Depending on the condition of the bill, it could be worth anything from $20 to $100.
Assuming it has a brown seal and says National Currency, about $25-35 depending on condition.
The Reserve Bank of Australia advises that there are approximately 132,600,000 Australian Twenty Dollar notes in circulation as at 30th of June, 2009.
The value of a 1928 twenty dollar bill that says "The Federal Reserve Missouri Bank of St. Louis" would actually depend on a number of things. The main factor that should be considered when determining value would be the condition of the bill.
$12 to $15, assuming average wear.
As of 09/2008 auction prices are around $24.
The issuing district on a twenty dollar bill can be found by looking at the first letter of the serial number on the bill. Different letters correspond to different Federal Reserve Banks, which are located in various cities across the United States.
Assuming it has a brown seal and is labelled "National Currency", your bill is worth $25 to $35 retail.
While the appearance of newer twenty dollar notes has changed, the 1993 $20 bill is, like more recent issues, a Federal Reserve Note and remains worth twenty dollars as legal tender in the United States. We know of no special or rare printings of the 1993 that might make a specimen worth more than its twenty dollar face value to collectors.
The US twenty dollar bill has not been discontinued.
The U.S. did not issue silver certificates with that denomination in 1934. For values of 1934 Federal Reserve Notes visit: http://www.uscurrencyauctions.com/$20notes.htm
Queen Elizabeth II is on the Canadian twenty dollar bill.
Australian twenty-dollar note was created in 1966.