Here is a list of the Top 100 Theorems of all time. A couple of economists make the list — Frank Ramsey, Joseph Bertrand — although not for economics theorems. I guess Arrow’s Impossibility Theorem, the Two Fundamental Theorems of Welfare Economics and the Folk Theorem for Repeated Games are unlikely to make a general list.
Here is a list of the Top 6 equations. I must say that I would have put E=mc2 at the top followed by Pythagoras which held that top spot for two millennia. I would also include Supply = Demand in the Top 5 of a general list but that might be just me.