What plants attract aphid predators?

Beneficial insects that prey on aphids, including ladybugs, lacewings, parasitic wasps, orius, and rove beetles, are drawn to plants with small, flat, open flowers. Good choices include alyssum, dill, yarrow, buckwheat, sunflowers, and cosmos. Planting these throughout your garden or farm creates a habitat that supports a natural population of aphid predators all season long.

On a larger scale, this practice is known as Farmscaping. Farmscaping is the intentional design of landscapes to attract and support beneficial insects. Ladybugs are a particularly valuable addition since they feed on the eggs of a wide range of pest species.

Want to go deeper? The ATTRA National Sustainable Agriculture Information Service offers an excellent free resource: 
Farmscaping to Enhance Biologicial Control covers how to design your growing space.