The card in Dominion that makes me happy is the Farming Village. The very existence of this card makes other cards much, much better.
Know all those terminal actions that are great because they're terminal? Goons, Wharf, Torturer, Witch, Council Room? With FV(aided by some trashing), these cards become Spamming Horses. Some cards become game-breakers:
Courtyard:Drawback? No drawback here. Play FV, then CY, putting a victory card back on the deck. Play FV again.
Envoy : Yowza, becomes a Sophie's Choice for your opponent(with some trashing, it quickly builds a fearsome engine)
Steward: Trash what you don't want, draw 2 more cards with the Actions you're piling up.
Bridge: No commentary necessary.
Comments?