Top recommendations:
Plants for clay soil
Agastache foeniculum 
Agastache scrophulariifolia 
Allium cernuum 
Amelanchier sp. - Serviceberry, Juneberry or Shadbush 
Asclepias incarnata 
Asters (see notes for particular sp.) 
Boltonia asteroides 
Chelone sp. - Turtlehead 
Clethra alnifolia - Sweet Pepperbush 
Cornus sp. - Dogwood 
Digitalis purpurea - Foxglove
Echinacea sp. - Purple Coneflower 
Echinops sp. - Globe Thistle
Eupatorium sp. - Joe Pye Weeds 
Helenium autumnale - Sneezeweed 
Heliopsis helianthoides - Ox Eye Daisy 
Helianthus sp. - Sunflowers 
Monarda sp. - Beebalm 
Physostegia virginiana - Obediant Plant 
Ratibida pinnata - Mexican Hat 
Rudbeckia laciniata
or Rudbeckia nitida - Yellow coneflower
Silphium perfoliatum - Cupplant 
Vernonia sp - Ironweed 
Viburnum sp. 
Zizia aurea - Golden alexander 
Plants for sandy soils (many of these plants also grow in clay soils)
Agastache sp - Hyssop 
Allium cernuum 
Astragalus canadensis - Canada Milk Vetch 
Blephilia ciliata - Wood mint 
Caryopteris sp. - Bluebeard
Calamintha nepeta - Dwarf Calamint
Cirsium discolor - Field Thistle 
Coreopsis sp. - Tickseed 
Dalea purpurea - Purple prairie clover 
Echinacea sp. - Purple coneflower 
Echinops sp - Globe Thistle
Erigeron sp. - Fleabanes 
Eryngium yuccifolium - Rattlesnake Master
Gaillardia sp. - Blanketflower 
Geum triflorum - Prairie smoke 
Helianthus sp. - Sunflowers 
Heliopsis helianthoides - Ox Eye Daisy 
Lavandula sp. - Lavender
Lobelia silphilatica - Great Blue Lobelia 
Lupinus perennis - Sundial lupine 
Monarda sp. - Beebalm 
Penstemon sp. - Bearded tongue 
Pycnanthemum sp. - Mountain Mint 
Ratibida pinnata - Mexican Hat 
Rubus odoratus - Purple flowering raspberry 
Rudbeckia hirta - Black eyed susan 
Solidago sp. - Goldenrod 
Scrophularia marilandica - Carpenter`s square 
Vernonia missurica - Missouri ironweed 
Vernonia gigantea - Tall ironweed 
Veronicastrum virginicum - Culvers Root 
Zizia aptera - Heartleaf Golden Alexander 