The first true commemoratives struck by the United States Mint were the 1892 and 1893 Columbian Exposition half dollars. The coins were to be sold at the World's Columbian Exposition in Chicago. The Exposition was originally scheduled to be held in 1892, but was postponed until 1893, hence the Exposition half dollars were struck in two different years. The event commemorated was of course Christopher Columbus' "discovery" of America in 1492.
The "souvenir coins," as they were called at the time, attracted a lot of attention from the public and the original mintages were huge compared to subsequent commemorative issues, 950,00 coins for the 1892 and 1,550,405 for the 1893. The initial sales price was $1 per coin, a figure that drew much criticism at the time, but nonetheless a great many were sold to the public at the Columbian Exposition.
Because they were widely distributed to the non-collecting public, many Columbian half dollars were not very well cared for. Also, the mintage was so large that values remained very low for decades. In the 1950's, circulated examples could be purchased for 60 cents. The 1892 and 1893 Colmbian half dollars are one of the most common 19th century U.S. coins. They are very easy to come by, especially in circulated condition. Gem MS65 examples are moderately scarce and Superb Gem examples are scarce.
Though the 1892 has a lower mintage than the 1893, it is actually a little easier to find in Gem and Superb Gem condition. The quality and eye appeal of uncirculated examples can vary greatly. The 1892 Columbians can be be frosty white to varying degrees, toned both beautifully or downright ugly and all the "shades" in-between, and (rarely) semi-prooflike. Some examples have very sharply struck sail and hair detail, others are somewhat weakly struck. The bottom line: look for attractive, well-struck examples, they are not that hard to find.