Depends on what you like really, but if your wife has a little gamer in her, you will have tons of fun with LittleBigPlanet.
Other than that, great games to get include Uncharted, Metal Gear Solid 4, Valkyria Chronicles, Motorstorm: Pacific Rift and others.
BUT! No matter what you do, you must buy Flower from the PS Store, it is an amazing game!