Treasure Map + Warehouse

This is totally killer combo and almost unstoppable.  You basically pick up two treasure maps as soon as possible and then use your warehouses to keep picking up more cards and discarding anything you have until you get the second treasure map in your hand.  Because the warehouse always gives you an extra action you will always be able to play another warehouse, if you can draw one, or play both treasure maps as soon as you have them in your hand.

This instantly gives you four gold cards to be drawn in your next hand.  If you get this combo to work near the first few turns of the game, then the game is basically for you to lose.  Just buy a province when you can, and if you can't then buy another gold.  Just make sure to keep your deck thin by avoiding buying other cards that aren't helpful.