It depends from cat to cat, so get an assortment. Jingle balls, things with feathers, and real fur mice are solid bets. The mice especially. They're made with rabbit fur and all of my cats love them. As others mentioned scratching posts are important, but also get a variety. Cardboard is a good bet, but cloth and rope are also good choices. If the cat starts scratching furniture, try redirecting to a scratcher or just put the scratcher next to the furniture.