What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
One major variety is the 1798/7 Draped Bust Large Cent (Penny) Overdate error. This coin features a 1798 date struck over a 1797 date which resulted in part of the underlying "7" appearing around and within the "8" as depicted by the arrows in the example image above. Source of example image is courtesy of Heritage Auction Galleries.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD