Lobelia

Any perennial that is tolerant of sun/part shade conditions will work perfectly well. And that does not limit you very much as there are scores of ones that would work :-) Like garden phlox, veronicastrum, lysimachia, most hardy geraniums, monarda, aconitum, actaea, aruncus, Siberian iris, columbine, etc., etc., etc. And pretty much any clematis will tolerate these conditions as well. You just want to avoid any full sun plants and those that prefer more shade, as afternoon sun is usually too strong for them

You would need to check on juglone tolerance, as that varies widely.

Thank you both for the suggestions! Gardengal, that's what I was hoping, and I'm glad to hear that I don't need to give up on a few favorites. Will definitely research the juglone issue for the other plants you mentioned.

Veronica, nepeta, salvia, scabiosa, geranium, iris, clematis, joe pye, windflower anemone, creeping phlox - not garden phlox sadly, Hosta, heuchara, Siberian squill, hyacinth, grape hyacinth, tulips, ornamental alium, daphne CM, liatris, actaea, and most sedums do well in my half sun beds that are chock full of juglone