Grand Market and Quarry
This all-Prosperity combo is probably the most potent of many variants of the Quarry+Market combo. The reason is two-fold: 1) Grand Market is one of the strongest cards in the game, and 2) Grand Market is difficult to buy early in most games, but Quarry gives you a fast-track method of grabbing a bunch.
This combo is pretty simple: Buy 2 or 3 Quarries, then start buying Grand Markets. Quarry reduces the price of Grand Markets, and Grand Market supplies the +Buys that go so well with playing Quarry. This snowballs quickly, so that you can buy 2 or 3 Grand Markets per turn. Once the Grand Markets run out, you are well positioned to either grab multiple Provinces or Colonies per turn, or buy out some cheap Action piles for a quick 3-pile ending when you are up.
This combo works decently with other Market variants, with the non-terminal +Buy being key - so look for cards like Market, Festival, Market Square, or even Pawn. With these lesser combos, it is necessary that you have other Actions you wish to stockpile - things like Conspirator, Peddler, City, and Laboratory make good targets.