I know you've been nose-to-the-grindstone since spring, but don't give up the ship just yet! Planting fall flowers can be the difference between a vibrant, exciting landscape and a big yawn. (yawn not lawn)
Plants that like the cool weather are the best candidates: Pansies, Mums (Chrysanthemums), Ornamental Kale, Johnny Jumpups... There are so many to choose from! Just try to remember those cold snowy days last winter when you couldn't play in the garden even if you wanted to and go out and enjoy one last round of planting that you will be able to enjoy for a few more weeks (to months) before the snow starts to fly.
Don't be a Pansy - Get your hands dirty!