"272 Days of Lowballs" - 1792 to 1964, 1 day per year. Could include Fair-2 coins to open up the number of replies a bit. Slabbed or raw but date must be readable.
"Presidents' Days" -- One day for coins/tokens/medals with images of every US President from Washington to LBJ (I think the ones since then are not likely to be on many coins.)
"Strange Days" -- US odd denomination type coins, 2c/3cs/3cn/20c/$3 gold/$4 gold, 1851 to whenever they quit making $3 and $4 gold
Days of Large Cents. 1793-1857. I would love this one and I know the big cents are pretty popular with many members.
"100 Days of Our Lives" -- Start with 1915 (to be fair!) Post your favorite coin that you own that was minted in the year of your birth, on the day for that year. If you were born in 1952, you'd post your favorite 1952-dated coin from your collection; same for 1970, 1988, whatever.
"Days of War" -- Post your favorite coins from the Revolutionary War, the War of 1812, the Civil War, the Spanish-American War, World War I, World War II, the Korean War, and the Vietnam war, with one day for each year that the US took part in those wars (e.g. 1861 to 1865 for Civil War).
"Days of Peace" --
Peace dollars 1921 to 1935 (short but fun)
Ones I would love to look at but can't participate in: maybe someday.
- Days of Saint Gaudens $20 Gold
- Days of Charlotte & Dahlonega minted gold
- Days of Pre-Civil-war Gold, 1793 to 1860
- Days of Proof
Morgan dollars