My world class collection of US coins would have to include the following: 1877 Indian Head Cent 1909 s VDB Lincoln Cent 1889 cc Morgan Dollar 1893 S Morgan Dollar 1907 Ultra High Relief St Gaudens Double Eagle 1916 Standing Liberty Quarter 1916 D Mercury Dime 1937 3 Leg Buffalo Nickel 1921 D Liberty Walker Can't believe I'm the first one to list the "King of the Morgans"!
My "world-class collection" would consist of every representative date/denomination from the Charlotte mint... it is a work in progress and I suspect I'll have to mortgage the house to afford the 1849-C Open Wreath $1... My Charlotte Collection http://coins.www.collectors-society.com/registry/coins/SetListing.aspx?PeopleSetID=22914
Now Charlottdude is the only person here who has described what to me could be a world class collection. The high grade keys that everyone else has described are for the most part readily available and lots of people have them. But a complete Charlotte date denomination set is not something you can just go out and put together. And there aren't going to be more than a few of them. THAT would be a world class collection. Who needs superior gems. my early date variety set averages G-4. Doesn't sound like much, but only a handful of people have sets that are more complete than mine. My set ranks as #13 in the national census. My draped bust set ranks even higher. World class? Probably.
I agree with Condor, that Charlotte Gold collection is much harder to put together than some of the key dates listed earlier. Some coins like 1909-s VDB is very common but highly priced, there are thousands of them around in high grades. 3 legged Buffalo is also easlier to find than most people think.
Maybe I need to be more clear about the "World Class" designation since it seems to be tripping people up. Here's the background. My grandfather just died at age 90 and it was mentioned that he had a coin collection. I haven't seen it yet, but it made me wonder what coins I could buy now in 2010 at age 40 that might be considered an "impressive" collection when I pass in 40 to 50 years? for example, look at the "recent appearances" section on this page. I mean, I could obtain a MS 65 red. Since it could be mentioned, does that make is on the list: http://www.coinfacts.com/small_cents/lincoln_cents/wheat_ear_cents/1909s_vdb_cent.htm
Those recent appearances are from 2000 and 2001. Looking at the Heritage Archives from 2009 and 2010, the prices realized are from a low of around $5000 to over $7000.
I'm working towards what I call a "denomination set" which would try to cover the history of U.S. coinage with exactly one coin per denomination. Here's the current end-game I'm shooting for: 1/2 cent -- 1809/6 This coin shows just how cavalier the mint could be about quality. It's not an overdate -- the 1806 half cent was of a different design. Just a blunder with a sloppy cover up job. 1 cent -- 1943-D Since 1943 cents are (so far), the only coins made of zinc-plated steel, this seems an obvious choice. My WWI and Denver mint representative. 2 cent -- 1864 Small Letters As made famous by "Who wants to be a millionaire," the first non-pattern with "In God We Trust." Civil war coin. 3 cent -- 1870 Silver Along with 1873, one of the two most bizarre years for U.S. Coinage. The U.S. minted two types of 3-cent pieces in 1870. The 3-cent silver was the lightest U.S. coin. 5 cent -- 1883 No-Cents Nickel To be a truly a world-class collection, this would need a Josh Tatum provenance. (Hey, I can dream, right?) 10 cent -- 1996-W The obvious (and only circulation design) for a coin from the West Point Mint. 15 cent -- 4th Issue, 1869-1875 Okay, it's a piece of fractional currency and not a coin. You don't like it, make your own collection. 20 cent -- 1875-cc I need a Carson City coin for the collection, and this is as good a spot as any. 25 cent -- 1917-S Standing Liberty (Type 1) Was there really a public outcry over Liberty's bare breast? I don't know, but it makes a good enough story that it makes it in as the representative from San Francisco. I'll pretend that I chose this over a 1916, since it's a WWI date. 50 cent -- 1861-O One of the very, very, few designs ever minted by 3 different sovereign entitles, and my representative of the New Orleans Mint. Peso -- 1936-M Roosevelt-Murphy The only territorial issue in the collection, a representative of the Manila Mint. 1 dollar -- 1880 Trade Dollar The only "proof-only" and only brilliant proof coin in the collection. Why 1880? Because I already own one. 2.5 dollar -- 1908 Matte Proof A matte proof, incuse design, and first year of issue. Who could ask for anything else? 3 dollar --1854-D The 2nd most expensive coin on the list. If I can't swing this one, I'll add an Dahlonega gold dollar and argue that a gold dollar wasn't the same denomination as a trade dollar. 4 dollar -- (none) Patterns? We don't need no steekin' patterns. 5 dollar -- 1861-C If I can't swing this one, I'll get another Charlotte issue. After all, I've already got the Civil War pretty well covered. 10 dollar -- 1799 Small Stars The collection needs an 18th Century representative, and this is it. The "Hey look! I'm a real country" Heraldic Eagle and the Small Stars are purely choices of personal preference. 20 dollar -- 1908 High Relief Any questions? 25 dollar -- Random Date I suppose I should include a gold bullion coin in here, and I do need a 21st century coin. 50 dollar -- 1915-S Octagonal The obvious choice. I don't expect to be able to swing this one, but it make the set world class. 100 dollar -- Random Date I suppose I should include a platinum bullion coin in here, and I do need a 21st century coin.