Members of the Composite or aster family are ideal. Examples are coneflowers, zinnias, marigolds, cosmos, black-eyed susans, and asters. Other good plants have clusters of small flowers, like butterfly weed, butterfly bush, alyssum, mints, verbena, and phlox. Most butterflies favor pink, lavender or purple blossoms, but some may visit other colors. For instance, swallowtails like reds and have been seen on yellow lantana.
Butterflies have a well developed sense of smell and are attracted to heavily perfumed flowers.
They will pass over lightly scented varieties in favor of the most fragrant. Heirloom and old-fashioned varieties tend to have a stronger scent. If you are interested in attracting moths, add sweet-smelling, night blooming flowers like nicotiana. Although a mix of flower types are good, large masses of one type are better than a bed with lots of varieties but only one or two plants of each type. For example, an entire bed of purple coneflowers will draw more butterflies than a single coneflower mixed in with other butterfly plants.