Got a bit lucky here, but buying a Province every single turn from 8-14 is pretty awesome.
http://dominion.isotropic.org/gamelog/201203/19/game-20120319-101221-3de38881.htmlJack+Hamlet is great, because it lets you cycle through the coppers, and gives +buy if you need it. It's basically Festival/Library except the buying power comes from the silvers.
Vault loves decks that are full of green and high-value money - so it works great with Jack, too. Though if your opponent is also using Jack, the option to discard is damaging. Still, good combo, I think.
Combine all three and you've got a pretty strong deck.