Asclepias verticillata is whorled milkweed for monarch caterpillars and butterflies, though its needle-thin leaves won't sustain hungry caterpillars for very long! The snow white blooms attract a variety of pollinators. More info and seeds.
Purple Milkweed can take a little longer to flower than other milkweed varieties, but it's worth the wait to finally see in all its purple glory. Get more info on growing Asclepias purpurascens for monarchs.