I'm on vacation moving my daughter from Brooklyn, NY to Minneapolis, MN and on the way taking a cat from Vermont to central Illinois to give to my ex. The topsoil in both Illinois and Minnesota is unbelievable: black and deep and good.
The prettiest plants in the tall grass prairies of Illinois are the Silphiums. Prairie Dock (Silphium terebinthinaceum) has interesting leathery leaves, even when they dry up and turn brown. Compass plant (Silphium laciniatum) has really neat looking, cut leaves.
The tall grasses themselves are beautiful now. My favorite tree I'm seeing everywhere in Minnesota is the Burr Oak or Quercus macrocarpa.