There are at least 4 major varieties of Large Cent from 1803.
Numismedia lists the following approximate retail values for the most common "small date" varieties, as of 05/2009:
Very worn condition - $65
Moderately worn - $200
Slightly worn - $400
Almost no wear - $1500
The rarer "large date" coins can sell for anywhere from $100 to $26,000 so regardless, it's best to have any 1803 cent inspected by a professional dealer or appraiser.
If your coin is a nickel please turn it over. The minting date is 2004, on the front. The date 1803 honors the Lewis and Clark expedition. If it's any other coin, pleas post a new, separate question with its denomination. You can also look for questions like "What is the value of an 1803 US <coin name>?", e.g. "What is the value of an 1803 US large cent?"
1 US cent has the same value the world over! i.e. 1 US cent
1856 3 cent coin value
About 1 cent.
It's still worth one cent US.
It's worth exactly one cent.
A 1997 US one cent piece? is a Lincoln cent and only face value.
A 1942 US Wheat cent is common, average value is 3 cents.
If you can't see the date 2004 on the front of the coin it must be in very bad condition but it's still worth five cents. The date 1803 is just part of the peace medal design on the reverse for that year.
The coin has face value only.
One cent, it's not that old
It's still worth one cent.