The big one is
Flying Eagle cent, but I might be getting one (or two) in mail soon (if I'm lucky). I suppose 1859
IHC too (that would be a lot harder).
Anything Seated Liberty or earlier. In particular, any
Half Dime, or anything with arrows and rays.
Any CC mint
Morgan dollar. (Any
Morgan dollar, really, but that's not quite dream territory because I could go and buy one right tomorrow - the only reason it's not right now is because it's half past midnight - and only use up a week's worth of food money.)
Any of the 1839 large cent varieties (especially the Silly and Booby heads). All of them, preferably (yes, even the ludicrously rare head of 1836), but that's getting really unlikely.
Any gold, obviously, but that's
way out of reach, unfortunately.
On the more local part, the cloud kopek is the big one. (I could probably afford a low-grade example already.) Ring kopek too, but that's a lot rarer. And the large date 2 kopek of 1797.
Also, any coins of False Dmitry, Vasily (non-Swedish), or Feodor III (or Vladislav if I could find any), but that doesn't really count because everyone has these coins for middling-high prices that I could easily pay if I wanted to, and I'm trying to find them cheaper. (And the 1596 kopek of Feodor I - Russia's oldest dated coin - in the same category.)