Collectible coins, particularly those from the United States, include various denominations such as the 1 cent (penny) and 50 cent (half dollar) coins. A notable example is the 1955 Proof Set, which was minted in Philadelphia. Proof Sets are specially made coins produced with a higher quality finish than regular coins, targeting collectors rather than general circulation. The 1955 Proof Set is particularly sought after due to its rarity and pristine quality, making it a valuable addition to any collection.