It depends on your house style:
If your house contains neutral and natural colors, a cactus really brings out a very native side.
If your house is somewhat Gilded Age looking (e.g. The Breakers) then fresh cut white roses add a touch of romance and wealthy charm.
If your house is contemporary, you can either go for extreme color with a bouquet of exotic flowers, or a stark rubber plant which adds shine and texture.
If your house is colonial and more laidback, daffodils or tulips in a long tall vase bring out the simple pleasures of country living.