Denominations can be as small as 1 cent. The highest face value I have seen is a $200 tax stamp used for paying the transfer tax on machine guns. A standard 1st class stamp is 49 cents.
.75
$0.20
Today (February 4, 2015) it is worth 80 cents US.
Worth 6 cents
The lowest value US stamp was the 1/2 cent. A couple different versions were issued.
8 cents.
The US issued a Chester W Nimitz stamp.
I have an old paper food stamp and i was wanting to know what it would be worth now. It's a 1999 $1.00 paper stamp. It's in great shape.
39 cents
Air mail stamps are good for ordinary postage- your stamp is still worth 7 cents if unused.
A US first class stamp dated 2002 is worth face value only, and it's still valid now.
50 cents if unused. Nothing if used.This must be the most common US airmail stamp.