Asclepias tuberosa - often recommended for monarchs, although I rarely see monarch caterpillars feeding on the ones in my yard, they seem to prefer other species of milkweed.
Asclepias syriaca - a very aggressive plant. Could be used if you have a meadow type planting, but frankly, you'll probably regret planting it in a typical yard
Ascelpias incarnata- mentioned above
Asclepias amplexicaulis - ditto
Asclepias viridiflora - seed is difficult to come by. Plants are rather, let's say, "unshowy"
Asclepias variegata - difficult to grow
Asclepias verticillata - another aggressive milkweed I wouldn't want to deal with in a yard or conventional flower bed. Not sure if monarchs feed on it or not, it's a slender plant with extremely narrow leaves, doesn't look like it would support a caterpillar the size of a monarch.
